System and method for focusing ultrasound image data

ABSTRACT

Sold-state intravascular ultrasound (IVUS) imaging devices, systems, and methods are provided. Some embodiments of the present disclosure are particularly directed to flexible and efficient systems for focusing IVUS echo data received from transducers including polymer piezoelectric micro-machined ultrasound transducers (PMUTs). In one embodiment, an ultrasound processing system includes first and second aperture engines coupled to an engine controller, which provides aperture assignments to the first and second aperture engines. The aperture engines receive the assignment and a portion of A-line data, perform one or more focusing process on the received A-line data, and produce focused data in accordance with the aperture assignment. In some embodiments, once an aperture engine has produced focused data, the engine controller clears the aperture engine and assigns another aperture.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and the benefit of U.S.Provisional Patent Application No. 61/693,118, filed Aug. 24, 2012,which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to intravascular ultrasound(IVUS) imaging and, in particular, to receiving and focusing ultrasoundinformation to produce an image. In various embodiments, the focusingsystem receives information from an array of ultrasound transducers,such as piezoelectric micromachine ultrasound transducers (PMUTs),capacitive micromachined ultrasonic transducers (CMUTs), andpiezoelectric zirconate transducers (PZTs). The focusing systemprocesses the data to produce an ultrasound image. For example, someembodiments of the present disclosure provide an IVUS imaging systemparticularly suited to imaging a human blood vessel.

BACKGROUND

Intravascular ultrasound (IVUS) imaging is widely used in interventionalcardiology as a diagnostic tool for assessing a diseased vessel, such asan artery, within the human body to determine the need for treatment, toguide the intervention, and/or to assess its effectiveness. An IVUSdevice including one or more ultrasound transducers is passed into thevessel and guided to the area to be imaged. The transducers emitultrasonic energy in order to create an image of the vessel of interest.Ultrasonic waves are partially reflected by discontinuities arising fromtissue structures (such as the various layers of the vessel wall), redblood cells, and other features of interest. Echoes from the reflectedwaves are received by the transducer and passed along to an IVUS imagingsystem. The imaging system processes the received ultrasound echoes toproduce a cross-sectional image of the vessel where the device isplaced.

There are two general types of IVUS devices in use today: rotational andsolid-state (also known as synthetic aperture phased array). For atypical rotational IVUS device, a single ultrasound transducer elementis located at the tip of a flexible driveshaft that spins inside aplastic sheath inserted into the vessel of interest. The transducerelement is oriented such that the ultrasound beam propagates generallyperpendicular to the axis of the device. The fluid-filled sheathprotects the vessel tissue from the spinning transducer and driveshaftwhile permitting ultrasound signals to propagate from the transducerinto the tissue and back. As the driveshaft rotates, the transducer isperiodically excited with a high voltage pulse to emit a short burst ofultrasound. The same transducer then listens for the returning echoesreflected from various tissue structures. The IVUS imaging systemassembles a two dimensional display of the vessel cross-section from asequence of pulse/acquisition cycles occurring during a singlerevolution of the transducer.

In contrast, solid-state IVUS devices carry a transducer complex thatincludes an array of ultrasound transducers distributed around thecircumference of the device connected to a set of transducercontrollers. The transducer controllers select individual transducersfor transmitting an ultrasound pulse and for receiving the echo signal.By stepping through a sequence of transmit-receive pairs, thesolid-state IVUS system can synthesize the effect of a mechanicallyscanned transducer element but without moving parts. Since there is norotating mechanical element, the transducer array can be placed indirect contact with the blood and vessel tissue with minimal risk ofvessel trauma. Furthermore, because there is no rotating element, theinterface is simplified. The solid-state scanner can be wired directlyto the imaging system with a simple electrical cable and a standarddetachable electrical connector.

Despite their wide acceptance, traditional solid-state IVUS imagingsystems have been held back by the processing required to form a focusedimage from the received echoes. Processing and focusing the ultrasounddata typically involves high-speed, high-performance computational coresconnected to large memory banks. Such hardware is expensive tomanufacture and has limited the quality of the image produced. Thus,while existing IVUS imaging systems have proven useful, there remains aneed for improved resolution and performance, particularly when it canbe delivered in a more economical system. Accordingly, the need existsfor improvements to solid-state IVUS signal processing systems.

SUMMARY

Embodiments of the present disclosure provide a high-performance,high-efficiency temporal focusing engine, which may be used inapplications such as a solid-state intravascular ultrasound imagingsystem.

In some embodiments, an ultrasound processing system is provided. Thesystem includes first and second aperture engines; an A-line datainterface providing at least a portion of A-line data to the first andsecond aperture engines; and an engine controller communicativelycoupled to the first and second aperture engines. The engine controllerprovides at least first and second aperture assignments designatingportions of the A-line data to the first and second aperture engines,respectively. The first and second aperture engines receive the firstand second aperture assignments, respectively, receive the at least aportion of the A-line data, perform one or more focusing processes onthe received A-line data, and produce focused data in accordance withthe first and second aperture assignments, respectively. In one suchembodiment, the engine controller further monitors to determine when oneof the first and second aperture engines produces focused data, andprovides a third aperture assignment to the one of the first and secondaperture engines when it is determined that the one of the first andsecond aperture engines has produced focused data.

In some embodiments, a method of focusing ultrasound echo data isprovided. The method comprises assigning a set of apertures to a set ofaperture engines, providing an ultrasonic dataset for one or moretransducer within the set of apertures to each of the aperture engineswithin the set of aperture engines, producing a focused A-line datasetwhen it is determined that a first aperture engine of the set ofaperture engines has sufficient data to produce the focused A-linedataset, and thereafter assigning another aperture to the first apertureengine.

In some embodiments, a system for processing echo data is provided. Thesystem comprises a means for performing focusing processes on an echodataset; a means for unimpededly providing at least a portion of theecho dataset communicatively coupled to the means for performingfocusing processes; and a means for performing a round-robin assignmentof apertures by providing configuration information designating portionsof the echo dataset to the means for performing focusing processes. Themeans for performing the round-robin assignment is communicativelycoupled to the means for performing focusing processes.

In some embodiments, an ultrasound system is provided, the systemcomprising a set of first-level aperture engines; a set of second-levelaperture engines communicatively coupled to one or more of the set offirst-level aperture engines; an A-line data interface providing atleast a portion of A-line data to each engine of the set of first-levelaperture engines; and an engine controller communicatively coupled toeach engine of the set of first-level aperture engines. The enginecontroller provides a sub-aperture assignment designating portions ofthe A-line data to each engine of the set of first-level apertureengines. The engines of the set of first-level aperture engines each:receive a provided sub-aperture assignment; receive the at least aportion of the A-line data; perform one or more first-level focusingprocess on the received A-line data; and produce partially-focused datain accordance with the provided sub-aperture assignment. The engines ofthe set of second-level aperture engines each: receive partially-focuseddata from the coupled engines of the set of first-level apertureengines, perform one or more second-level focusing processes on thereceived partially-focused data, and produce focused aperture data. Inone such embodiment, the engine controller further monitors to determinewhen one engine of the set of first-level aperture engines producespartially focused data, and provides another sub-aperture assignment tothe one engine of the set of first-level aperture engines when it isdetermined that the one engine has produced partially-focused data.

In some embodiments, a method of focusing ultrasound echo data isprovided, the method comprising: assigning a set of sub-apertures to aset of first-level aperture engines; providing at least a portion of anultrasonic dataset to each engine of the set of first-level apertureengines; producing a partially-focused A-line dataset when it isdetermined that a first first-level aperture engine of the set offirst-level aperture engines has sufficient data to produce thepartially-focused A-line dataset; thereafter assigning anothersub-aperture to the first first-level aperture engine; receiving thepartially-focused A-line dataset at a first second-level aperture engineof the set of second-level aperture engines; and producing a focusedA-line dataset when it is determined that the first second-levelaperture engine has sufficient data to produce the focused A-linedataset.

In some embodiments, a system is provided comprising: a bump mapgenerator receiving a transducer configuration specifying aemitter/receiver transducer pair and producing a bump map based on thetransducer configuration; a clock signal generator producing afixed-frequency clock having a clock frequency; and an analog-to-digitalconverter that performs: receiving analog data corresponding to theemitter/receiver transducer pair; and producing digital data based onthe analog data having a sample rate determined by the fixed-frequencyclock and the bump map.

In some embodiments, a method is provided comprising: receiving analogecho data corresponding to an emitter/receiver transducer pair;receiving a fixed-frequency reference clock having a clock frequency;receiving a transducer configuration based on the emitter/receivertransducer pair; determining a bump map from the transducerconfiguration; and digitizing the analog echo data to produce digitalecho data. The digital echo data has a sampling interval determined bythe fixed-frequency reference clock and the bump map.

In some embodiments, an ultrasound processing system is provided. Thesystem comprises a digital data interface receiving digital ultrasoundecho data; and a frequency converter communicatively coupled to thedigital data interface. The frequency converter receives the digitalultrasound echo data and a measure of resolution for a display image andresamples the digital ultrasound echo data to produce resampled digitalultrasound echo data having a sampling interval based on the measure ofresolution.

In some embodiments, a method is provided comprising: receiving digitalultrasound echo data; receiving a measure of resolution for a displayimage; and resampling the digital ultrasound echo data based on themeasure of resolution.

In some embodiments, a system for resampling ultrasound data isprovided. The system comprises a signal interface receiving anultrasound data stream; a coefficient interface receiving a set ofweighting coefficients; and a weighted interpolation networkcommunicatively coupled to the signal interface and the coefficientinterface. The weighted interpolation network includes a plurality ofdelay devices delaying the ultrasound data stream, wherein the delayingproduces a plurality of delayed ultrasound data streams; a plurality ofweighting units applying the set of weighting coefficients to theplurality of delayed ultrasound data streams, wherein the applyingproduces a plurality of weighted ultrasound data streams; and a summingunit adding the plurality of weighted ultrasound data streams to producea resampled ultrasound data stream.

In some embodiments, a method of processing ultrasound data is provided.The method comprises: receiving digital ultrasound data; delaying thedigital ultrasound data by a first delay amount to produce first delayeddigital ultrasound data; applying a first weighting to the first delayeddigital ultrasound data to produce first weighted ultrasound data;delaying the digital ultrasound data by a second delay amount to producesecond delayed digital ultrasound data; applying a second weighting tothe second delayed digital ultrasound data to produce second weightedultrasound data; and adding the first and second weighted ultrasounddata to produce resampled digital ultrasound data.

In some embodiments, an ultrasound processing system is provided. Thesystem comprises: first and second baseband aperture engines; an A-linedata interface providing at least a portion of A-line data to the firstand second aperture engines; and an engine controller communicativelycoupled to the first and second aperture engines. The engine controllerprovides first and second aperture assignments designating portions ofthe A-line data to the first and second aperture engines, respectively.The first and second baseband aperture engines receive the first andsecond aperture assignments, respectively; receive the at least aportion of the A-line data, perform one or more baseband focusingprocesses on the received A-line data; and produce focused data inaccordance with the first and second aperture assignments, respectively.In one such embodiment, the engine controller further monitors todetermine when one of the first and second baseband aperture enginesproduces focused data, and provides a third aperture assignment to theone of the first and second baseband aperture engines when it isdetermined that the one of the first and second baseband apertureengines has produced focused data.

In some embodiments, a method of focusing ultrasound echo data isprovided. The method comprises: assigning a set of apertures to a set ofbaseband aperture engines; providing an ultrasonic dataset for one ormore transducer within the set of apertures to each of the basebandaperture engines within the set of baseband aperture engines; producinga focused A-line dataset when it is determined that a first engine ofthe set of baseband aperture engines has sufficient data to produce thefocused A-line dataset; and thereafter assigning another aperture to thefirst engine.

Some embodiments of the present disclosure incorporate a parallelarrangement of aperture engines performing focusing calculationsaccording to round-robin aperture assignments in order to achieve highresource utilization and optimal throughput. The parallel arrangement offocusing engines takes advantage of the highly parallel nature offocusing processes. In some embodiments, the aperture enginesselectively obtain echo data from a common bus based on the apertureassignment, which avoids the need for data steering circuitry. Thesimplified data bus allows for more implementation options. For example,in some embodiments, each aperture engine is implemented on a separatelow-cost device such as an ASIC, FPGA, DSP, microcontroller, or CPU,whereas, in some embodiments, multiple aperture engines are implementedon a single device, such as an ASIC, FPGA, DSP, microcontroller, or CPU.

Further embodiments utilize a hierarchical arrangement of parallelaperture engines to divide focusing computations. This configurationallows further flexibility in implementation. For example, in someembodiments, lower level focusing is performed near to the transducers,such as in the transducer complex or on the wire. Digitization of echodata close to the transducers may reduce line loss and transmissionnoise, and such embodiments may also simplify the interface between theIVUS device and the remainder of the IVUS system. In some embodiments,lower-level engines are part of a sterile package and operate within asterile field, while upper level engines are located outside the sterilefield, such as in an adjacent observation area. The simplified interfaceof a hierarchical arrangement reduces the number of wires that cross thesterile boundary. In embodiments utilizing a wireless interface,potential avenues for contamination are further reduced.

Various embodiments utilize intelligent resampling to reduce the datasetrequired to represent digitized echo data. In some embodiments, thisreduces data handling thereby allowing reductions in bus width, busspeed, bus buffering, and/or data storage. In some embodiments, reduceddata size allows reduction in processing resources allocated to focusingtasks such as time-of-flight adjustment, apodization, and summation. Inturn, this may deliver smaller, more economical, and moreenergy-efficient implementations.

Some embodiments of the present disclosure reduce the size of the echodataset without adversely affecting the quality of the focused echo databy utilizing variable-rate digitization of analog echo data. In someembodiments, variable-rate digitization is performed utilizingfixed-rate components through the use of a bump map. This implementationmay convey additional advantages as fixed-rate components may draw lesspower, may avoid complex control circuitry, and may exhibit improveddurability and longevity when compared to variable-rate equivalents.

Some embodiments of the present disclosure reduce the size of the echodataset by accounting for the resolution of the final image. The finalimage is composed of pixels, which are regions of uniform color andintensity. Accordingly, in some embodiments, data beyond an amountneeded to determine a pixel can be discarded without affecting the finalimage. This can result in improved efficiency, reduced system size, andreduced cost. In an embodiment, per-pixel resampling allows a mid-rangeimaging system to produce a high-resolution image such one configuredfor a high-definition display.

Some embodiments of the present disclosure manage the size of the echodataset by performing an interpolated phase shift as an alternative toupsampling. The interpolated phase shift provides increased datagranularity without the higher data rate associated with upsampling. Insome embodiments, this retains the benefits of the lower bit-ratesincluding lower clock frequencies, reduced data steering, decreasedcircuit complexity, and reduced memory requirements. As anotheradvantage, certain focusing steps may benefit from increased datagranularity while others may benefit from lower bit rates. Instead ofresampling prior to each focusing step, in some embodiments, theinterpolated phase shift replaces an upsampling process followed by adownsampling process.

Further embodiments extend the round-robin architecture and schedulingto baseband focusing of echo data. Because baseband representations ofecho data have lower characteristic frequencies, digital sampling ratescan be reduced. The reduced sampling rate may accordingly reduce busspeed, data storage requirements, clock frequency, power consumption,and/or processing hardware required for other focusing steps.

Additional aspects, features, and advantages of the present disclosurewill become apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present disclosure will be describedwith reference to the accompanying drawings, of which:

FIG. 1 is a diagrammatic schematic view of an imaging system accordingto aspects of the present disclosure.

FIG. 2 is a flow diagram of a method of generating ultrasound dataaccording to aspects of the present disclosure.

FIG. 3 is a radial cross-sectional view of a portion of a transducercomplex according to aspects of the present disclosure.

FIG. 4 is a radial cross-sectional view of a portion of a transducercomplex according to aspects of the present disclosure.

FIG. 5 is an aperture diagram of a transducer complex according toaspects of the present disclosure.

FIG. 6 is a radial cross-sectional view of a portion of a transducercomplex according to aspects of the present disclosure.

FIG. 7 is a flow diagram of a method of collecting ultrasound data formultiple apertures concurrently according to aspects of the presentdisclosure.

FIG. 8 is a plot of received transducer echo data over time according toaspects of the present disclosure.

FIGS. 9a and 9b are schematic diagrams of variable-clock-rate digitizersaccording to aspects of the present disclosure.

FIG. 10 is a flow diagram of a method of generating variable-ratedigitized ultrasound data according to aspects of the presentdisclosure.

FIG. 11 is a cross-sectional view of a focused aperture of a transducercomplex according to aspects of the present disclosure.

FIG. 12 is a schematic of a focusing system according to aspects of thepresent disclosure.

FIG. 13 is a schematic of an aperture engine according to aspects of thepresent disclosure.

FIG. 14 is a schematic of a TOF and apodization unit according toaspects of the present disclosure.

FIG. 15 is an illustration of an ultrasound image produced by anintravascular ultrasound imaging system according to aspects of thepresent disclosure.

FIG. 16 is a plot of received transducer echo data over time accordingto aspects of the present disclosure.

FIG. 17 is a schematic of a resampling device according to aspects ofthe present disclosure.

FIG. 18 is a schematic of a resampling network according to aspects ofthe present disclosure.

FIG. 19 is a flow diagram of a method of resampling ultrasound dataaccording to aspects of the present disclosure.

FIG. 20 is a flow diagram of a method of producing focused datautilizing an aperture engine according to aspects of the presentdisclosure.

FIG. 21 is a schematic of a focusing system according to aspects of thepresent disclosure.

FIG. 22 is a flow diagram of a method for focusing multiple aperturesaccording to aspects of the present disclosure.

FIG. 23 is a schematic of a focusing system according to aspects of thepresent disclosure.

FIG. 24 is a schematic of a hierarchically arranged focusing systemaccording to aspects of the present disclosure.

FIG. 25 is a flow diagram of a method for performing hierarchicalfocusing according to aspects of the present disclosure.

FIGS. 26a and 26b are schematic diagrams of baseband modulatorsaccording to aspects of the present disclosure.

FIG. 27 is a schematic of a baseband aperture engine according toaspects of the present disclosure.

FIG. 28 is a flow diagram of a method of baseband aperture focusingaccording to aspects of the present disclosure.

FIG. 29 is a schematic of a baseband focusing system according toaspects of the present disclosure.

FIG. 30 is a flow diagram of a method for focusing multiple aperturesaccording to aspects of the present disclosure.

FIG. 31 is a flow diagram of a method of utilizing the IVUS deviceaccording to aspects of the present disclosure.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thepresent disclosure, reference will now be made to the embodimentsillustrated in the drawings, and specific language will be used todescribe the same. It is nevertheless understood that no limitation tothe scope of the disclosure is intended. Any alterations and furthermodifications to the described devices, systems, and methods, and anyfurther application of the principles of the present disclosure arefully contemplated and included within the present disclosure as wouldnormally occur to one skilled in the art to which the disclosurerelates. For example, while the focusing system is described in terms ofcardiovascular imaging, it is understood that it is not intended to belimited to this application. The system is equally well suited to anyapplication requiring imaging within a confined cavity. In particular,it is fully contemplated that the features, components, and/or stepsdescribed with respect to one embodiment may be combined with thefeatures, components, and/or steps described with respect to otherembodiments of the present disclosure. For the sake of brevity, however,the numerous iterations of these combinations will not be describedseparately.

FIG. 1 is a diagrammatic schematic view of an intravascular ultrasound(IVUS) imaging system 100 according to aspects of the presentdisclosure. In some embodiments of the present disclosure, the IVUSimaging system 100 is a piezoelectric micromachine ultrasound transducer(PMUT) solid-state IVUS imaging system. In some embodiments, the IVUSimaging system 100 is a CMUT or PZT solid-state IVUS imaging system. TheIVUS imaging system 100 may include an IVUS device 102 such as acatheter, guide wire, or guide catheter, a patient interface module(PIM) 104, an IVUS processing system or console 106, and/or a monitor108.

At a high level, the IVUS device 102 emits ultrasonic energy from atransducer complex 110 near the tip of the device. The ultrasonic energyis reflected by structures within the environment surrounding thetransducer complex 110. The transducer complex 110 also receives andmeasures the reflected waves.

The PIM 104 facilitates communication of signals between the IVUSconsole 106 and the IVUS device 102 to control the operation of thetransducer complex 110. This includes transferring echo data detected bythe transducer complex 110 to the IVUS console 106. In that regard, thePIM 104 forwards the echo data received and, in some embodiments,performs preliminary processing of the echo data prior to transmittingthe data to the console 106. In examples of such embodiments, the PIM104 performs amplification, filtering, and/or aggregating of the data.In an embodiment, the PIM 104 also supplies high- and low-voltage DCpower to support operation of the device 102 including circuitry withinthe transducer complex 110.

The IVUS console 106 receives the echo data from the transducer complex110 by way of the PIM 104 and processes the data to create an image ofthe environment surrounding the transducer complex 110. The console 106may also display the image on the monitor 108.

In some embodiments, the IVUS device includes some features similar totraditional solid-state IVUS catheters, such as the EagleEye® catheteravailable from Volcano Corporation and those disclosed in U.S. Pat. No.7,846,101 hereby incorporated by reference in its entirety. For example,the IVUS device 102 includes the transducer complex 110 at a distal endof the device 102 and a transmission line bundle 112 extending along thelongitudinal body of the device 102. The transmission line bundle 112terminates in a PIM coupler 114 at a proximal end of the device 102. ThePIM coupler 114 electrically couples the transmission line bundle 112 tothe PIM 104 and physically couples the IVUS device 102 to the PIM 104.In an embodiment, the IVUS device 102 further includes a guide wire exitport 116. Accordingly, in some instances the IVUS device is arapid-exchange catheter. The guide wire exit port 116 allows a guidewire 118 to be inserted towards the distal end in order to direct thedevice 102 through a vessel 120. Vessel 120 represents fluid filled orsurrounded structures, both natural and man-made, within a living bodythat may be imaged and can include for example, but without limitation,structures such as: organs including the liver, heart, kidneys, gallbladder, pancreas, lungs; ducts; intestines; nervous system structuresincluding the brain, dural sac, spinal cord and peripheral nerves; theurinary tract; as well as valves within the blood or other systems ofthe body. In addition to imaging natural structures, the images may alsoinclude imaging man-made structures such as, but without limitation,heart valves, stents, shunts, filters and other devices positionedwithin the body, for example, a guide wire or guide catheter. In anembodiment, the IVUS device 102 also includes an inflatable balloonportion 122 near the distal tip. The balloon portion 122 is open to aduct that travels along the length of the IVUS device and ends in aninflation port (not shown). The balloon 122 may be selectively inflatedand deflated via the inflation port.

The IVUS processing system 106 is designed to operate in conjunctionwith the IVUS device 102 to produce high-resolution images from withinnarrow passageways. To advance the performance of IVUS imaging devicescompared to the current state of the art, embodiments of the presentdisclosure incorporate advanced transducer technologies, such as PMUT,that offer wide bandwidth (>100%) and a spherically-focused aperture.The broad bandwidth is important for producing a short ultrasound pulseto achieve optimum resolution in the radial direction, and thespherically focused aperture provides optimum resolution in the lateraland elevation dimensions. The improved resolution provided by PMUT andother advanced ultrasound transducer technologies facilitates betterdiagnostic accuracy, enhances the ability to discern different tissuetypes, and enhances the ability to accurately ascertain the borders ofthe vessel lumen. Embodiments of the present disclosure also provide animproved focusing engine within the IVUS processing system 106, whichimproves focusing resolution, reduces noise and artifacts, and deliversincreased resolution and frame rate while utilizing more efficient andmore economical components.

A method of collecting ultrasound data is described with reference toFIGS. 2, 3, and 4. FIG. 2 is a flow diagram of a method 200 ofgenerating ultrasound data according to aspects of the presentdisclosure. It is understood that additional steps can be providedbefore, during, and after the steps of method 200, and some of the stepsdescribed can be replaced or eliminated for other embodiments of themethod. FIGS. 3 and 4 are radial cross-sectional views of a portion of atransducer complex 110 according to aspects of the present disclosure.

The transducer complex 110 houses an array of transducers 302, thirteenof which are illustrated in FIG. 3. The transducers 302 are grouped intoapertures 304, including apertures 304 a, 304 b, and 304 c. In someembodiments, each transducer 302 may be part of one or more apertures304. For example, transducer 302 c is included in apertures 304 a, 304b, and 304 c. By way of non-limiting example, in the illustratedembodiment, each aperture 304 contains nine transducers 302. Otheraperture widths are contemplated. For example, further embodiments haveapertures 304 containing 8, 10, 12, 14, 16, or 32 transducers 302. In anembodiment, an aperture 304 contains 128 transducers 302.

Referring to block 202 and FIG. 3, the aperture 304 and the associatedtransducers 302 within the aperture are identified. This may includedetermining which particular transducer is located at each end of theaperture. Referring to FIG. 3, for exemplary aperture 304 a, transducer302 a is at a first end, and transducer 302 i is located at a secondend. In block 204, initial emitting and receiving transducers aredesignated. Groupings of emitting and receiving transducers are referredto as A-lines. Within an A-line, more than one emitting transducer andmore than one receiving transducer may be configured to act together.Furthermore, in some embodiments, a transducer may be designated as bothan emitting and a receiving transducer. Accordingly, in an exemplaryfiring, transducer 302 a is both the initial emitting transducer and theinitial receiving transducer.

In block 206, the designated emitting transducer (in the currentexample, transducer 302 a) or transducers are triggered to emitultrasonic energy. A portion of the ultrasonic energy (e.g., the portiondirected along the line indicated by arrows 306) is reflected by atarget structure 308 located in the environment surrounding thetransducer complex 110. In block 208, the designated receivingtransducer (in the current example, transducer 302 a) or transducersreceive the reflected ultrasonic echo (indicated by arrows 310 a). Forthe purposes of this disclosure, the act of receiving by a transducermay include experiencing an energy impulse such as an ultrasonic echo,converting the received impulse into a signal such as an electricpotential, transmitting the converted signal, measuring the convertedsignal, and/or other suitable receiving steps. In some embodiments, aplurality of emitting transmitters is fired as a group. Firingtransducers as a group may create a stronger ultrasonic transmission.Particularly in, but not limited to, embodiments using relatively smallemitting transducers and/or embodiments imaging relatively longdistances, a stronger emission improves the signal-to-noise ratio.Similarly, in some embodiments, a plurality of receiving transducers isset to receive as a group. The group of transducers may produce astronger electrical potential with a better imaging characteristics thanindividual transducers acting alone.

In the illustrated embodiment, a sequence of firings are produced foreach emitting transducer using a series of receiving transducers. Thereceiving transducers are stepped through according to a walk pattern.An exemplary walk pattern, which may be designated a forward walk,advances transducers in an arbitrary first direction (e.g., fromtransducer 302 a to 302 b to 302 c). A backward walk advancestransducers in a direction opposite the first direction (e.g., fromtransducer 302 c to 302 b to 302 a). Other walk patterns utilize morethan one direction, skip transducers, repeat transducers, grouptransducers and/or operate according to any other suitable pattern. Whenthe receive cycle is complete, the next emitting transducer is selected.

Accordingly, in block 210, it is determined whether the currentreceiving transducer or transducers are the final transducer in the walkpattern. In some exemplary pattern, the final transducer in the patternis the transducer at an end of the aperture (e.g., transducer 302 aand/or transducer 302 i for aperture 304 a). In some exemplary patterns,the final receiving transducer is the emitting transducer. If thereceiving transducer is not the final transducer in the pattern, inblock 212, the next receiving transducer or transducers are designatedaccording to the walk pattern. In the embodiment depicted in FIG. 3,according to a forward walk pattern, transducer 302 b is designated asthe next receiving transducer.

From block 212, the transmit and receive sequence of blocks 206 and 208is repeated using the newly designated transmitter and receiver pair. Inthe illustrated embodiment of FIG. 3, an emission from transducer 302 a(indicated by arrows 306) is reflected by the target structure 308. Thereflection is received and converted by transducer 302 b (indicated byarrows 310 b). In the next iteration, emissions from transducer 302 aare received by transducer 302 c (indicated by arrows 310 c). Thisproceeds until the forward walk pattern reaches transducer 302 i(indicated by arrows 310 i), which is the final receiving transducer inthe aperture 304 a. This completes the receive cycle for emittingtransducer 302 a.

Upon completion of the receive cycle, the method proceeds from block 210to block 214 where it is determined whether the emitting transducer ortransducers are the final emitting transducer according to an emitterwalk pattern. In some embodiments, the final emitting transducer in thepattern is the transducer at an end of the aperture. If the emittingtransducer is not the final transducer, in block 216, the next emittingtransducer is designated. In some embodiments, this includes modifyingan aspect of the receiver walk pattern as well. The walk pattern of thereceiving transducers may be switched, for example, by switching from aforward walk pattern to a backward walk pattern. A new receivingtransducer may also be designated. For example, the receiving transducermay be changed from transducer 302 i to 302 a when the emittingtransducer changes. Other embodiments incorporate further modificationsto the receive sequence.

Referring now to FIG. 4, in the illustrated embodiment, transducer 302 bis designated the next emitting transducer, and the receiver walkpattern is switched to a backward walk pattern. In this embodiment, thedesignated receiving transducer, 302 i, remains unchanged. In block 206,emitting transducer 302 b creates an ultrasound emission (indicated byarrows 406), which is reflected by the target structure 308 and receivedby transducer 302 i (indicated by arrows 410 i). Because of the backwardwalk pattern, in the next iteration, the emissions from transducer 302 bare received by transducer 302 h (indicated by arrows 410 h) andsubsequently transducer 302 g (indicated by arrows 410 g). The methodcontinues until final emitting transducer has completed a receive cycle,and, in some embodiments, the A-line combinations of emittingtransducers and receiving transducers within the aperture are exhausted.

It is understood that disclosing the method 200 in terms of steppingthrough receiving transducer for a designated emitting transducer ispurely arbitrary. In some embodiments, a receiving transducer isdesignated and the method 200 proceeds through a sequence of emittingtransducers before designating a new receiving transducer. Furthermore,the emitter and receiver walk patterns disclosed with reference to FIGS.3-4 are examples selected for clarity of illustration. Other walkpatterns are contemplated and provided for.

As can be seen, for each of the exemplary nine-transducer apertures 304,81 transducer combinations (or A-lines) exist. In some embodiments, thenumber of A-line firings is reduced by assuming that A-line dataexhibits a reciprocal nature. In other words, a signal emitted bytransducer 302 a and received by transducer 302 i may be a suitablesubstitute for a signal emitted by transducer 302 i and received bytransducer 302 a. Thus, in some embodiments, only one A-line for eachreciprocal A-line pair is generated.

FIG. 5 is an aperture diagram 500 of a transducer complex 110 accordingto aspects of the present disclosure. FIG. 5 illustrates therelationship between transducer pairs (A-lines) and the associatedapertures and the relationship between adjacent apertures. As can beseen, the aperture diagram 500 of FIG. 5 leverages the reciprocal natureof the data to reduce the number of A-line firings. In the illustratedembodiment, for an aperture having N transducers and an initialtransducer index of i, signals generated by transducer T_(i) arereceived by each transducer between T_(i) and T_(i+N−1) inclusive.Signals generated by a subsequent transducer T_(i+1) are received byeach transducer between T_(i+1) and T_(i+N−1) inclusive, but notnecessarily by T_(i) because suitable substitute data from T_(i) toT_(i+1) exists. Accordingly, the signal generated by T_(i+N−1) isreceived by T_(i+N−i), but not necessarily at the other transducers. Putin the context of FIG. 5, a first exemplary nine-transducer apertureincludes transducers T_(A) through T_(I) and is represented by triangle502 a. Signals generated by transducer T_(A) are received by transducersT_(A) through T_(I). Signals generated by transducer T_(B) are receivedby transducers T_(B) through T_(I), and so on. As can be seen, thefiring pattern incorporates only 45 firings instead of 81. This canmeasurably reduce the time required to obtain an aperture dataset.

FIG. 6 is a radial cross-sectional view of a portion of a transducercomplex 110 according to aspects of the present disclosure. In someembodiments, data collection is expedited by collecting data formultiple apertures 304 simultaneously. As previously noted, eachtransducer may be part of more than one aperture, and accordingly, eachA-line (transducer combination) may be part of more than one aperture.A-lines from transducer 302 b received at transducers 302 b through 302i are part of apertures 304 a and 304 b. A single additional A-linemeasurement 610 j from transducer 302 b to transducer 302 j issufficient to provide complete datasets for both apertures with regardto emitting transducer 302 b. Accordingly, in an embodiment, the firingpattern of transducer 302 b generates the data required for bothapertures 304 a and 304 b.

Referring back to FIG. 5, the first exemplary nine-transducer apertureincludes transducers T_(A) through T_(I), as indicated by triangle 502a. A second adjacent aperture includes transducers T_(B) through T_(J)as indicated by triangle 502 b. Accordingly, in an embodiment, duringthe receive cycle of emitting transducer T_(B), an additional firing isperformed for receiving transducer T_(J). This produces data for thefirst and second apertures 502 a and 502 b. Furthermore, the receivecycle for emitting transducer T_(C) includes receiving transducers T_(C)through T_(K) to produce data for the first and second apertures 502 aand 502 b as well as a third represented by triangle 502 c. In otherwords, for a given aperture having N transducers and an initialtransducer index of i, signals generated by transducer T_(i) arereceived at each transducer between T_(i) and T_(i+N−1) inclusive.Signals generated by transducer T₁₊₁ are received at each transducerbetween T_(i+1) and T_(i+N) inclusive, despite the fact that T_(i+N) isnot included in the first aperture. The sequence continues until thefull dataset for the given aperture has been collected, at which timepartial data will have been collected for N−1 other apertures. Someembodiments take advantage of concurrent collection of data pertainingto multiple apertures to perform aperture processing in parallel. As anexample, signal data for transducer T_(c) is used in apertures 502 a,502 b, and 502 c. Thus, in some embodiments, the signal data fortransducer T_(c) may be processed for apertures 502 a, 502 b, and 502 cconcurrently.

FIG. 7 is a flow diagram of a method 700 of collecting ultrasound datafor multiple apertures 304 concurrently according to aspects of thepresent disclosure. It is understood that additional steps can beprovided before, during, and after the steps of method 700, and some ofthe steps described can be replaced or eliminated for other embodimentsof the method 700. Referring to block 702, an aperture 304 and theassociated transducers 302 within the aperture are identified. This mayinclude identifying transducers located at each end of the aperture. Inblock 704, initial emitting and receiving transducers are designated. Inone embodiment, a transducer at an end of the aperture is designated asboth the first emitting and the first receiving transducer. In block706, the designated emitting transducer or transducers are triggered toemit ultrasonic energy. In block 708, the designated receivingtransducer or transducers receive the reflected ultrasonic echo andconvert the received energy into echo data. In block 710, the echo datais provided for processing in multiple apertures, such as the aperturesthat contain the designated transducers.

In block 712, it is determined whether a designated receiving transduceris the final transducer in the walk pattern. If the receiving transduceris not the final transducer in the walk pattern, in block 714, the nextreceiving transducer or transducers are designated according to thepattern. In some such embodiments, advancing in a first direction isdesignated as a forward walk, while advancing in a second direction isdesignated as a backward walk. The transmit and receive sequence ofblocks 706 and 708 is repeated using the newly designated transmitterand receiver group.

If, in block 712, the receiving transducer is the final transducer inthe pattern, the receive cycle is completed for the emitting transducer.Upon completion of the receive cycle, the method proceeds from block 712to block 716 where it is determined whether a current emittingtransducer is the final transducer in the emitter walk pattern. If not,in block 718, the next emitting transducer or transducers aredesignated. In block 718, the next receiving transducer or transducersmay be designated as well, according to the receiver walk pattern. Insome embodiments, in block 720, the walk pattern is modified (e.g.,alternated between a forward walk and a backward walk). The method thenproceeds to block 714.

The method 700 continues until the final emitting transducer of anaperture has completed a receive cycle. When this occurs, the method 700proceeds from block 716 to block 722, where the focused A-line data forthe aperture is transmitted. The method 700 then proceeds to block 718,where the emitting and receiving transducers are incremented and datacollection is performed for subsequent apertures. Even where this datacollection method does not improve the time to collect the firstaperture dataset, it may reduce the time required to obtain thesubsequent aperture datasets because of the concurrent collection ofdata pertaining to multiple apertures.

It is understood that disclosing the method 700 in terms of steppingthrough receiving transducer for a designated emitting transducer ispurely arbitrary. In some embodiments, a receiving transducer isdesignated and the method 700 proceeds through a sequence of emittingtransducers before designating a new receiving transducer. Furthermore,the walk patterns disclosed are examples selected for clarity ofillustration. Other walk patterns are contemplated and provided for.

FIG. 8 is a plot of received transducer echo data 802 over timeaccording to aspects of the present disclosure. In many embodiments,analog transducer echo data 802 is digitized for further processing in adigital domain. Digitization often includes taking samples of the analogdata at discrete points in time as indicated by lines 804. Thisdigitization may be performed within an IVUS device 102, within a PIM104, within an IVUS processing system 106, and/or at another suitablelocation within another IVUS component. In some embodiments,digitization is performed using a fixed-clock-rate digitizer. Thisproduces a fixed number of digital samples per increment of time.However, memory, processing resources, and processing time may bereduced by sampling echo data frequently during a period when echo datais expected to arrive at the receiving transducer and less frequently ornot at all elsewhere. Thus, in some embodiments, digitization isperformed using a variable-frequency digitizer. This may reduce thenumber of samples in the digitized echo data and may reduce the systemrequirements to process the echo data.

Referring to FIG. 8, a sampling pattern for the echo data may contain aninitial period 806 when the signal produced by a receiving transducer isnot relevant. Accordingly, samples during the initial period 806 may beomitted. For example, this initial period 806 may correspond to a timewhen the reflection of the ultrasonic emission has not yet arrived, andtherefore any measurement is background noise. The sampling pattern mayalso contain one or more active periods 808 and 810 when the echo data802 is sampled at a varying frequencies. In an embodiment, during afirst active period 808 when the signal data is less relevant, the datais sampled at a relatively lower frequency than during a second activeperiod 810. Many factors may affect data relevance. For example, periodscorresponding to a focal range outside of a range of interest may be ofless relevance. As a further example, periods corresponding to dataproduced before the emitter reaches peak output may exhibit a reducedsignal-to-noise ratio and thus be less relevant. The sampling patternmay account for these relevance factors and others. In variousembodiments, the timing and duration of the active periods 808 and 810as well as the sampling rates during the active periods are selected tobalance sample size and data quality.

Variable-frequency sampling can be performed utilizing avariable-frequency oscillator. In such embodiments, the simplicity ofthe digitizer design must be balanced against possible drawbacks. Forexample, variable-frequency oscillators may require complicated controllogic, may require more power than fixed-frequency oscillators, maygenerate more heat than fixed-frequency oscillators, and may havereduced reliability.

FIGS. 9a and 9b are schematic diagrams of variable-clock-rate digitizersaccording to aspects of the present disclosure. The digitizer 900 ofFIG. 9a incorporates a fixed-rate oscillator 902 and a bump mapgenerator 904. The digitizer 900 receives analog echo data 906 alone orin conjunction with a transducer configuration 908 of the A-line used toproduce the echo data 906. For example, the transducer configuration 908may indicate the A-line or emitter/receiver pair that generated the echodata 906. From the transducer configuration 908, the bump map generator904 determines a sampling pattern for echo data.

The sampling pattern may be based on a geometry of a transducer complex110 (e.g., degree of curvature, transducer spacing, distance betweenemitter and receiver, length of signal lines, etc.), a characteristic ofa transducer (e.g., firing delay, sensitivity etc.), a characteristic ofan aperture (e.g., width, location on the transducer complex, etc.),and/or other relevant factors that affect arrival time, signal quality,signal relevance, etc. In an exemplary embodiment, A-lines having asingle transducer acting as both emitter and receiver may have a shorterdistance to and from a target structure than transducer pairs spacedfurther apart. The sampling pattern may be structured accordingly. Inanother exemplary embodiment, the sampling pattern accounts formanufacturing variances. In various other embodiments, the temporallocation of the sampling pattern accounts for other effects, bothmeasured and calculated, that affect the time at which the echo data isreceived.

In some embodiments, the total number of samples is determined by areference A-line. In one such embodiment, the bump map for a referenceA-line specifies a total of 3000 samples. In the embodiment, bump mapsfor other related A-lines specify the same number of total samples,although the arrangement in time may vary.

The sampling pattern can be used to align echo data 906 collected fromvarious A-lines within an aperture. In some embodiments, this isperformed by selecting the periods of the sampling pattern including theinitial period 806 to perform the temporal alignment of echo data 906between A-lines. In some embodiments, the sample rates of the periods ofthe sampling pattern are calculated to perform the temporal alignment ofecho data.

The bump map generator 904 creates a bump map 910 corresponding to thesampling pattern. In some embodiments, the bump map 910 includes abinary data (0s and 1s) where a 1 indicates that a sample of the analogdata should be taken at the corresponding clock pulse and a 0 indicatesthat a new sample should not be taken at the corresponding clock pulse.In alternate embodiments, a 1 indicates that a new sample should not betaken at the corresponding clock pulse and vice versa.

The bump map 910 and the clock produced by the fixed-rate oscillator 902are provided to the analog-to-digital converter 912. Theanalog-to-digital converter 912 samples the analog echo data at theclock rate determined by the combination of the clock and the bump map910. In some embodiments, the bump map 910 masks the clock. For example,the bump map 910 and the clock may be supplied as inputs to an AND-gatewithin the analog-to-digital converter 912. The output of the AND-gatecan serve as sample clock used to by the analog-to-digital converter 912to sample the analog echo data. In this way, the analog-to-digitalconverter 912 produces digitized echo data 914 from the analog echo data906 having a sample frequency determined by the combination of the clockand the bump map 910.

The digitizer 950 of FIG. 9b also incorporates a fixed-rate oscillator902 and a bump map 910. Digitizer 950 is substantially similar todigitizer 900, except as noted. One distinction is that the digitizer950 incorporates an analog-to-digital converter 912 that samples at afixed frequency based on the clock generated by the fixed-rateoscillator 902. As with a fixed-rate oscillator, a fixed-frequencyanalog-to-digital converter may be less complicated, may consume lessenergy, may generate less heat, and/or may be more reliable than avariable-rate alternative. Accordingly, digitizer 950 may have reducedsize, complexity, and/or power consumption, and may have improvedreliability compared to alternative designs.

The analog-to-digital converter 912 produces fixed-rate digitized echodata 952, which is converted to variable-rate digitized data 956 by arate converter 954 according to the bump map 910. In doing so, the rateconverter 954 may perform downsampling, upsampling, interpolation,and/or other modifications to the fixed-rate data 952. Accordingly, insome embodiments, the rate converter 954 discards samples from thefixed-rate digitized echo data 952 to produce the variable-ratedigitized echo data 956. In some embodiments, the rate converterresamples and thereby adds samples to the fixed-rate digitized echo data952. In some embodiments, the rate converter interpolates values fromsamples of the fixed-rate digitized echo data 952 to produce thevariable-rate digitized echo data 956.

FIG. 10 is a flow diagram of a method 1000 of generating variable-ratedigitized ultrasound data according to aspects of the presentdisclosure. It is understood that additional steps can be providedbefore, during, and after the steps of method 1000, and some of thesteps described can be replaced or eliminated for other embodiments ofthe method 1000. Referring to block 1002, analog echo data is receivedfrom an A-line transducer group. The analog echo data may be receiveddirectly from the transducers 302 of the A-line or from an amplifier, afilter, a signal conditioner, and/or other suitable interface system. Inblock 1004, a fixed frequency reference clock is received. The frequencyof the reference clock may correspond to a maximum sampling frequency tobe used during the generation of the variable-rate digitized data. Inblock 1006, a transducer configuration is received that specifies someaspect of the A-line. The transducer configuration may specify thetransducers of the A-line, a geometry of a transducer complex 110, acharacteristic of a transducer, a characteristic of an aperture, and/orother relevant factors from which temporal characteristics of the echodata can be determined.

In block 1008, a bump map is determined from the transducerconfiguration. The bump map specifies the sampling intervals of thedigitized echo data, and may be used to specify an initial intervalduring which the analog echo data is not sampled, active intervalsduring which the echo data is sampled at a reduced frequency, activeintervals during which the echo data is sampled at an increasedfrequency, and other critical time intervals.

In some embodiments, the intervals are selected to provide an increasedsampling rate during a period where echo data is expected. By reducingthe number of samples elsewhere, the bump map may reduce the memory,processing resources, clock speeds, and power consumption used for datahandling and focusing. In some embodiments, the bump map coordinates thetotal number of samples between multiple A-lines. For example, the totalsamples may be set by a reference A-line, and bump maps for otherA-lines in the aperture may conform to the reference total. In someembodiments, the bump map is used to perform a temporal alignment ofecho data across A-lines.

In some embodiments, the bump map includes a sequence of binary data (0sand 1s) where a 1 indicates that a sample of the analog data should betaken at the corresponding clock pulse and a 0 indicates that a newsample should not be taken at the corresponding clock pulse. Inalternate embodiments, a 1 indicates that a new sample should not betaken at the corresponding clock pulse.

In block 1010, the analog echo data is digitized according to thereference clock and the bump map to produce the variable-rate digitalecho data. In some embodiments, the bump map is used to gate thereference clock and produce a variable-rate clock for sampling. Infurther embodiments, the analog data is first digitized by sampling atthe reference clock frequency, and the fixed-frequency data isdownsampled, upsampled, interpolated, and/or otherwise modifiedaccording to the bump map. Utilizing a bump map allows the digital echodataset to be reduced without adversely affecting data quality andwithout the use of variable-frequency devices that may requirecomplicated control logic, may require more power than fixed-frequencyequivalents, and may demonstrate reduced reliability.

FIG. 11 is a cross-sectional view of a focused aperture 304 of atransducer complex 110 according to aspects of the present disclosure.Once the aperture data is collected, it may undergo a mathematicalfocusing process. Focusing improves image quality by adjusting andcombining data collected from the A-line transducer combinations. Theeffect of focusing is to combine the A-line data into a dataset thatsimulates a narrow-width emission from a location within the aperture304 and received at a location on the transducer complex 110, regardlessof whether transducers 302 actually exist at these locations or whethersuch a narrow-width emission could be produced. In some embodiments,more than one focused A-line is produced per aperture 304. The differentfocused A-lines may be directed at different angles from the surface ofthe transducer complex 110. For example, focusing may produce data forA-lines 1102 a, 1102 b, and 1102 c. These different focused A-lines maybe referred to as different flavors of focused A-line data. In someembodiments, the focusing calculations are range sensitive. For example,a given focused A-line (e.g., A-line 1102 a) may be calculated using oneset of factors for range 1104 a, another set for 1104 b, and another for1104 c. In further non-limiting examples, a given focused A-line iscalculated for other numbers of ranges 1104 including 2, 4, 5, 6 and 9.In an embodiment, the number of ranges 1104 is the number of samplescollected for a measured (not focused) A-line. Other suitable numbers ofranges are provided for. Thus, focusing may include sets of calculationsdivided by range, flavor, and/or other aspects of the focused A-line tobe produced.

The process of focusing may include space-time alignment of data (radialfocusing, a radial direction indicated by arrow 1106) as well as spatialalignment of data (azimuthal focusing, an azimuthal direction indicatedby arrow 1108). The first type of alignment, space-time alignment, mayinclude time-of-flight adjustment. Due to different flight paths betweenA-lines, received echoes may arrive at the transducers at differenttimes. Time-of-flight adjustment shifts the received responses in timeto align the signals with those of other A-lines within the aperture.The second type of alignment, spatial alignment may include amplitudebalancing and apodization. One type of amplitude balancing applies anamplitude adjustment to the received responses based on characteristicsof the transducers. For example, a transducer may have reducedsensitivity to signals directed at oblique angles. Thus, a directionalamplification factor may be determined based on the receivingtransducer's location relative to the emitting transducer. In a furtherexample, an adjustment may be applied to correct for a less-sensitivetransducer such as one that may result from a manufacturing variance.Apodization is another type of amplitude weighting and may be used toreduce grating and side lobe effects and other artifacts from theimaging process. Apodization may include tapering off the amplitude of areceived response on either side of a window of time. This emphasizesthe response during the peak of the window. Exemplary apodizationweightings include boxcar, Hann, Hamming, cosine, root-raised-cosine,and half-cosine window functions.

FIG. 12 is a schematic of a focusing system 1200 according to aspects ofthe present disclosure. Portions of the focusing system 1200 may beincorporated into an IVUS processing system 106, a patient interfacemonitor (PIM) 104, and/or other components of an IVUS imaging system100. In various embodiments, the focusing system 1200 focuses A-linedata from the transducers 302 within an aperture 304 to produce afocused dataset for the aperture 304. Focusing system 1200 receivesA-line data 1202 via an A-line data steering interface 1204. In someembodiments, the interface 1204 receives the A-line data 1202 from atransducer complex 110. In some such embodiments, the A-line interface1204 receives data directly from transducers 302 of the transducercomplex 110. In some embodiments, the A-line interface 1204 receivesdata from a memory subsystem such as a data buffer, an analog-to-digitalconverter, an analog and/or digital amplifier, a filter, a signalconditioner, and/or other suitable interface systems. The A-line datasteering interface 1204 directs the received data to the appropriatetime-of-flight (TOF) adjustment unit 1206.

The time-of-flight adjustment units 1206 align the A-line data in time.In the illustrated embodiment, the focusing system 1200 includes atime-of-flight adjustment unit 1206 for each A-line in the aperture,although only four are illustrated for the sake of clarity. Otherembodiments incorporate as few as one time-of-flight adjustment unit1206. The time-of-flight adjustment unit or units 1206 align the A-linedata by shifting the signal in time according to an offset. In someembodiments, the particular offsets applied by the units 1206 aredetermined based on a geometry of the transducer complex 110 (e.g.,degree of curvature, transducer spacing, distance between emitter andreceiver, length of signal lines, etc.), a characteristic of atransducer (e.g., firing delay, sensitivity etc.), a characteristic ofan aperture (e.g., width, location on the transducer complex, etc.),and/or other relevant factors that affect arrival time. In someembodiments, such as when a focused A-line is broken up into more thanone calculation based on a distance range 1104 or flavor, discretetime-of-flight offsets are supplied for each particular focal range 1104or flavor. In some embodiments, time-of-flight offsets are determined byanalysis of the incoming A-line data through a method such as peakdetection either in addition to or as a replacement for utilizingpre-determined values. After the offset is applied, the aligned A-linedata is supplied to the apodization units 1208.

Apodization units 1208 apply a set of amplitude weightings to correctfor grating and side lobe effects. Such weighting typically taper offthe amplitude of a received response on either side of a window of timeand may be derived from apodization functions such as a boxcar, Hann,Hamming, cosine, root-raised-cosine, half-cosine window function and/orother suitable apodization function. The apodization units 1208 may alsoperform an amplitude adjustment based on transducer characteristics. Forexample, the amplitude adjustment may correct for a transducer withreduced sensitivity. The resulting aligned and apodized data is providedto a summing unit 1210, which adds the data from the unfocused A-linesto produce focused A-line data for the aperture.

FIG. 13 is a schematic of an aperture engine 1300 according to aspectsof the present disclosure. Portions of the aperture engine 1300 may beincorporated into an IVUS processing system 106, a patient interfacemonitor (PIM) 104, and/or other components of an IVUS imaging system100. In some embodiments, the aperture engine 1300 leverages theparallel nature of the focusing calculations to improve focusingthroughput. In contrast to focusing system 1200, aperture engine 1300incorporates a running sum unit 1306 and a streamlined interface incombination with a parallelized architecture. In the illustratedembodiment, the aperture engine 1300 performs N parallel calculations offocused A-line data, of which three are shown. Further embodimentsincorporate other numbers of TOF and apodization units 1304 and runningsum units 1306 to produce other number of flavors. For example, in onesuch embodiment, the aperture engine 1300 includes a single TOF andapodization unit 1304 and a single running sum unit 1306.

The aperture engine 1300 receives raw A-line data for focusing. Thisdata may be received from a transducer complex 110, a memory subsystem,an analog-to-digital converter, an analog and/or digital amplifier, afilter, a signal conditioner, and/or other suitable interface systems.The received A-line data 1302 is then distributed to one or moretime-of-flight (TOF) and apodization units 1304. In the illustratedembodiment, each unit 1304 corresponds to a subset of focused A-linedata. In various examples, the subsets are divided by range and/orflavor, although obviously other divisions are provided for. Each TOFand apodization unit 1304 receives a set of TOF adjustments 1308 andapodization coefficients 1310. The values of the TOF adjustments 1308and apodization coefficients 1310 within the set may be determined basedon the subset of focused A-line data assigned to the TOF and apodizationunit 1304. For example, a first set of TOF adjustments 1308 andapodization coefficients 1310 may be correspond to a first flavor andrange combination. The units 1304 may then align the A-line data samplesin time according to the TOF adjustment factors 1308 and may apply anapodization function and/or amplitude balancing according to theapodization coefficients 1310.

The aligned and apodized A-line data produced by the one or more TOF andapodization units 1304 is input into a corresponding running sum unit1306. The running sum unit 1306 adds the aligned and apodized data forthe A-lines that make up the aperture. When the running sum unit 1306has accumulated sufficient data, the unit 1306 produces the focusedA-line data 1312. This data 1312 may be a subset (e.g., select flavorsand/or ranges) of the total focused A-line data for the aperture. Byproviding multiple TOF and apodization units 1304 and running sum units1306, the aperture engine 1300 is thus able to produce multiple subsetsof data 1312 concurrently.

In addition to the advantages of parallelization, another advantage tothis architecture is that, in some embodiments, the A-line data isdistributed to any number of TOF and apodization units 1304 without adata steering interface. This streamlined interface may allow thecircuitry for generating each data subset (including the associated TOFand apodization unit 1304 and running sum unit 1306) to be implementedon a separate computing hardware device (e.g., a general purposeprocessor, a graphic processing unit, an ASIC, an FPGA, a DSP, amicrocontroller, etc.). In the alternative, in some embodiments, thecircuitry for calculating multiple data subsets is implemented on asingle computing hardware device. Furthermore, in some embodiments, theelimination of steering circuitry allows the complete aperture engine1300 to be implemented on a single computing hardware device. In thisway, the present disclosure provides a scalable aperture engine 1300capable of producing focused A-line datasets corresponding to multipleflavors, ranges, or other division simultaneously, and provides anefficient interface that allows for single-chip as well as multiple-chipimplementations.

FIG. 14 is a schematic of a TOF and apodization unit 1400 according toaspects of the present disclosure. The TOF and apodization unit 1400 issuitable for use in an aperture engine 1300 such as that disclosed withreference to FIG. 13. The TOF and apodization unit 1400 includes atime-of-flight adjustment unit 1206 and an apodization unit 1208substantially similar to those described with reference to FIG. 12. TheTOF and apodization unit may also include a pre-TOF resample unit 1402and/or a pre-apodization resample unit 1404. In various embodiments, theresample units 1402 and 1404 are used to condition data by upsamplingand/or downsampling.

The pre-TOF resample unit 1402 may perform the variable ratedigitization and/or the variable-rate conversion of the A-line datadisclosed with reference to FIG. 9. In such embodiments, the pre-TOFresample unit 1402 may receive a bump map 910 that designates a samplingpattern. The sampling pattern may be based on a geometry of a transducercomplex 110 (e.g., degree of curvature, transducer spacing, distancebetween emitter and receiver, length of signal lines, etc.), acharacteristic of a transducer (e.g., firing delay, sensitivity etc.), acharacteristic of an aperture (e.g., width, location on the transducercomplex, etc.), and/or other relevant factors that affect arrival time,signal quality, signal relevance, etc. The total number of samples inthe sampling pattern may be determined based on a reference A-line. Forexample, bump maps for related A-lines may designate sampling patternshaving the same number of total samples, although the arrangement intime may vary. The sampling pattern may also align echo data collectedfrom various A-lines within an aperture. As an alternative to receivinga bump map 910 that designates the sampling pattern, the pre-TOFresample unit 1402 may receive parameters used to determine the bump map910.

In some embodiments, the pre-TOF resample unit 1402 is used to improvethe accuracy of the time-of-flight adjustment by increasing theeffective sample rate of the A-line data. Resampling achieves some ofthe benefits of a higher sampling rate without the extensive hardwarerequirements associated with higher data rates. The pre-TOF resampleunit 1402 may also be used to apply a time-of-flight adjustment eitherin addition to or as a replacement for the adjustment applied in the TOFadjustment unit 1206.

In an exemplary embodiment, A-line data sampled at 200 megasamples/secis received at the pre-TOF resample unit 1402. The pre-TOF resample unit1402 resamples the A-line data at 4× thereby providing A-line datasampled at 800 megasamples/sec to the TOF adjustment unit 1206. Anysuitable resampling algorithm including any suitable resampling filtermay be used to resample the data. Resampling algorithms are known tothose of skill in the art. Non-limiting examples of resamplingalgorithms include linear interpolation, Lagrange interpolation, cubicspline interpolation, polyphase interpolation, and/or other suitablealgorithms. In some such embodiments, the pre-TOF resample unit 1402receives a set of resample coefficients 1406 specifying a resamplingrate, coefficients for a resampling algorithm, and/or other resamplingconfiguration data.

As an alternative to performing a full upsample of the A-line data, insome embodiments, the pre-TOF resample unit 1402 performs aninterpolated phase shift. An interpolated phase shift produces outputdata at the same sample rate as the input data, but time shifted so thatthe samples corresponds to shifted points in time. For example, a 4×interpolated phase shift may produce phase shifts of 0°, 90°, 180°, and270°. Given input A-line data with samples at integer values of time(e.g., 1, 2, 3, 4, 5, 6, etc.), a phase shift of 90° would produceoutput A-line data at the same sample rate but with samplescorresponding to amplitude values at times 1.25, 2.25, 3.25, 4.25, etc.These intermediate amplitude values may be calculated using any suitableresampling algorithm. A phase shift of 180° would produce output A-linedata at the same sample rate but with samples corresponding to amplitudevalues at 1.5, 2.5, 3.5, 4.5, etc. A phase shift of 270° would produceoutput A-line data corresponding to values at 1.75, 2.75, 3.75, 4.75,etc. This phase shift provides increased data granularity without thehigher data rate. To provide further data granularity, a phase shiftsequence, such as (180°, 90°, 0°, 270°, 180°, 0°), may be used toproduce output A-line data at the same sample rate as the input but withsamples corresponding to amplitude values at times, such as 1.5, 2.25,3, 4.75, 5.5, 6, etc.

In various embodiments, interpolation retains the benefits of the lowerbit-rates such as lower clock frequencies, reduced data steering,decreased circuit complexity, and/or reduced memory requirements.Furthermore, as can be seen, this phase shift may be incorporated aspart of the time-of-flight adjustment. In some embodiments and for someA-line configurations, this phase shift may suffice to align the datasuch that no further time-of-flight adjustment is needed. Anotheradvantage is that some embodiments, certain focusing steps benefit fromincreased data granularity while others do not. Accordingly, performinga single interpolated phase shift may avoid an upsampling processfollowed by a downsampling process.

To provide further data granularity, in some embodiments, the phaseshift may vary for each sample. For example, a phase shift sequence(180°, 90°, 0°, 270°, 180°, 0°) may be used to produce output A-linedata at the same sample rate as the input but with samples correspondingto amplitude values at times 1.5, 2.25, 3, 4.75, 5.5, 6.

In various embodiments, the pre-TOF resample unit 1402 receives a set ofresample coefficients 1406 specifying a resample rate, specifying aphase shift, specifying coefficients for an interpolation algorithm,and/or specifying other resampling configuration data. In someembodiments, the pre-TOF resample unit 1402 performs thefixed-to-variable rate echo data conversion described with reference toFIGS. 9a and 9b . In such embodiments, the resample coefficients 1402may include a bump map 910 and/or configuration data from which a bumpmap 910 may be determined.

The pre-apodization resample unit 1404 may perform an upsampling and/oran interpolated phase shift substantially similar to that described withrespect to the pre-TOF resample unit 1402. Alternatively, in someembodiments, the pre-apodization resample unit 1404 performs adownsampling of the time-of-flight adjusted echo data. Whereas focusingmay benefit from increased accuracy created by interpolation,apodization and weighting may not. In some embodiments, apodizationaccuracy is not improved for any sample rate beyond a threshold based inpart on the resolution of the final image.

FIG. 15 is an illustration of an ultrasound image 1500 produced by anintravascular ultrasound imaging system 100 according to aspects of thepresent disclosure. From image 1500 a skilled operator can identifystructures including the transducer complex 110, borders of a vessel1502, a plaque 1504, blood 1506, and/or other structures of interest.Digital images including image 1500 are comprised of a set of pixels1508 (enlarged for clarity). As pixels 1508 are areas of uniform colorand intensity, data beyond an amount needed to determine color and/orintensity for a pixel can be discarded without affecting the final image1500. For a hypothetical A-line (e.g., the A-line represented by dashedline 1510), it can be determined how many pixels 1508 are intersectedand accordingly how many samples are needed. In some embodiments, thesampling rate is determined based on a ratio of samples per pixel. Inone such embodiment, A-line data is sampled at a rate of one sample perpixel. Sampling based on a ratio of samples per pixel may be referred toas per-pixel resampling or pixel-aware resampling. Omitting samples thathave no effect on the final image per-pixel resampling may allow areduction in computing hardware, for example the apodization unit 1208,as the dataset being manipulated is smaller. This can result in improvedefficiency, reduced system size, and reduced cost. In an embodiment,per-pixel resampling allows a mid-range imaging system to produce ahigh-resolution image such one configured for a high-definition display.

As the image 1500 is a Cartesian representation of a polar dataset, theintersections of the A-lines and the pixels may be calculated or a setof Cartesian and/or polar approximations may be used. Cartesianapproximations may rely on trigonometric principles to determine aunique number of samples for each A-line based on the angle. A-linesdirected perpendicular to a row or column of pixels (e.g., horizontaland vertical A-lines) will intersect the fewest number of pixels,whereas A-lines directed at 45° to a perpendicular A-line can be assumedto intersect the most. Accordingly, in some embodiments using aCartesian approximation, perpendicular A-lines will be resampled to havea first number of samples while the number of samples for other A-lineswill be based on an angle relative to a perpendicular A-line. In anexemplary polar approximation, each focused A-line is resampled at thesame number of samples. The particular number of samples is determinedby an archetypal A-line. The archetypal A-line may be an A-line havingthe most intersections, an average (mean or median) number ofintersections, or other suitable number of intersections. Theseexemplary approximations are not limiting, and embodiments utilizingother suitable approximations are contemplated and provided for. Forexample, in some embodiments, an area-based approximation apportions thetotal number of pixels for the image 1500 among the A-lines, where thenumber of samples per A-line corresponds to the total number of pixelsin the image divided by the total number of focused A-lines.

In some embodiments, the pixel-to-sample relationship is reevaluatedwhen operating parameters change. For example, increasing thefield-of-view may increase the number of samples per image while thenumber of pixels in the image remains the same. Accordingly, thepixel-to-sample ratio may be recalculated as field-of-view changes.Other operating parameters may affect the number of samples collected orfocused, the resolution of the image, and/or the target sample-to-pixelratio.

FIG. 16 is a plot of received transducer echo data 1600 over timeaccording to aspects of the present disclosure. The transducer echo data1600 is sampled at discrete points in time as indicated by lines 1602.This digitization may be performed within an IVUS device 102, within aPIM 104, within an IVUS processing system 106, and/or at anothersuitable location within another IVUS component. In the illustratedembodiment, the points in time 1602 are determined based on a resolutionof a final image. For example, the points in time 1602 are determinedbased on a ratio of samples per pixel such as 1:1. In some embodiments,the samples are not at fixed intervals and instead correspond to analignment of an A-line relative to one or more pixels.

Referring again to FIG. 14, in an embodiment, the pre-apodizationresample unit 1404 receives a set of resample coefficients 1408, whichmay include a resampling rate, interpolation coefficients, a phaseadjust, a number of samples, an image or display resolution, a ratio ofsamples per pixel, and/or other resampling configuration data. Thepre-apodization resample unit 1404 resamples the time-of-flight adjusteddata according to the resample coefficients 1408 and provides theresampled data to the apodization unit 1208. The apodization unit 1208may then perform apodization and amplitude modification on the resampledA-line data substantially as described with reference to FIG. 12, forexample.

One of skill in the art will recognize that additional processingincluding, but not limited to, resampling may be performed on theadjusted A-line data produced by the apodization unit 1208. For example,in some embodiments, pixel-aware resampling is performed on the adjustedA-line data. This may reduce the processing required for subsequentimage formation steps. As another example, in some embodiments,filtering is performed on the adjusted A-line data produced by theapodization unit 1208. Further processing steps will be known to thoseskilled in the art.

FIG. 17 is a schematic of a resampling device 1700 according to aspectsof the present disclosure. The resampling device 1700 is suitable foruse in a pre-time-of-flight resample unit 1402 and/or a pre-apodizationresample unit 1404 such as those described with respect to FIG. 14. Theillustrated resampling device 1700 is a type of polyphase interpolationdevice. The resampling device 1700 receives an input data stream 1702such as a set of A-line data and distributes it through a set of delayelements 1704 to produce a set of delayed data streams. In theillustrated embodiments, the delay elements 1704 are chained to in orderproduce the set of delayed data. In some embodiments, chainedimplementations reduce the size and/or complexity of the individualdelay elements 1704 that make up the network. In other embodiments,separate parallel delay elements 1704 are used to allow greater controlover each delay magnitude.

Weighting elements 1706 apply weighting factors to the set of delayeddata streams and the resulting weighted data streams are summed by thesum element 1708 to produce the resampled data stream 1710. Theweighting factors applied by the delay elements 1706 determine therelationship of the resampled data stream 1710 and the input data stream1702. In some embodiments, the resampling device 1700 performs afiltering function such as a bandpass, low-pass, and/or high-passfiltering. In one such embodiment, the resampling device 1700 performs alow-pass filtering by utilizing weighting factors derived from a sincfunction. This is useful for eliminating high frequency noise introducedby some methods of resampling. The resampling device 1700 may also beused to perform a partial phase shift. For example, the weightingfactors may be chosen to perform phase shifts of 0°, 90°, 180°, and/or270°. In one embodiment, resampling device 1700 receives weightingfactors corresponding to a phase shift selected based on a geometry of atransducer complex 110, a characteristic of a transducer, acharacteristic of an aperture, and/or other relevant factors.

FIG. 18 is a schematic of a resampling network 1800 according to aspectsof the present disclosure. The resampling network 1800 is suitable foruse in a pre-time-of-flight resample unit 1402 and/or a pre-apodizationresample unit 1404 such as those described with respect to FIG. 14. Theresampling network 1800 may include one or more resampling devices 1700such as the resampling device 1700 described with respect to FIG. 17.The resampling devices 1700 each receive an input data stream (forexample, an input A-line data stream) and a set of weighting factors1802. The sets of weighting factors 1802 may differ between devices1700. The resampling network 1800 also includes a multiplexer 1804 thatdetermines which of the resampled data streams is selected as the outputdata stream. In this manner, the multiplexer 1804 selects betweendifferently weighted and resampled versions of the input data stream.

In an exemplary embodiment, a resampling network 1800 includes fourresampling devices 1700. A data stream corresponding to an A-linetransducer pair is received at the resampling devices 1700 along with aset of weighting factors 1802. The four sets of weighting factorscorrespond to phase shifts of 0°, 90°, 180°, and 270° relative to thesample period of the data stream. Accordingly, the resampling devices1700 produce weighted resampled data streams corresponding to the fourphase shifts. The multiplexer 1804 is used to select the appropriatephase shift to output based on factors such as a geometry of atransducer complex 110, a characteristic of a transducer, acharacteristic of an aperture, and/or other relevant factors. In anembodiment, a phase shift sequence is supplied to the multiplexer 1804(e.g., a sequence representing 180°, 90°, 0°, 270°, 180°, 0°), and isused by the multiplexer 1804 to produce output A-line data at the samesample rate as the input but with samples corresponding to amplitudevalues at times 1.5, 2.25, 3, 4.75, 5.5, 6.

Such a resampling network 1800 can perform the pre-TOF resamplingdescribed with respect to the pre-TOF resample unit 1402 of FIG. 14. Byproducing a phase shifted version of the input data stream having thesame sampling frequency as the input data stream, the resampling network1800 provides the greater data granularity of upsampling withoutincreased data-handling overhead associated with higher samplingfrequencies. The result is a lightweight, efficient datapath withimproved data accuracy.

FIG. 19 is a flow diagram of a method 1900 of resampling ultrasound dataaccording to aspects of the present disclosure. It is understood thatadditional steps can be provided before, during, and after the steps ofmethod 1900, and some of the steps described can be replaced oreliminated for other embodiments of the method 1900. Referring to block1902, an ultrasound echo data stream is received. The ultrasound echodata stream may correspond to A-line echo data. In block 1904, theultrasound data is delayed by a first delay amount to produce a firstdelayed data stream. In block 1906, a first weighting value is appliedto the first delayed data stream in order to produce a first weighteddata stream. The first weighting value may be part of an interpolationfilter. For example, the weighting value may be based on a sincfunction. The first weighting value may also contain a phase shiftcomponent.

In block 1908, the ultrasound data is delayed by a second delay amountto produce a second delayed data stream. In block 1910, a secondweighting value is applied to the second delayed data stream. Similar tothe first weighting value, the second value may have a component basedon an interpolation filter, and/or a component based on a phase shift.In block 1912, the first and second weighted data are added to produce aresampled ultrasound data stream. In some embodiments, the procedures ofblocks 1902 through 1912 are performed multiple times in parallel toproduce multiple resampled ultrasound data streams. A resampled datastream may be selected from the multiple streams according to an aspectof the A-line that produced the analog data stream such as a geometry ofa transducer complex 110, a characteristic of a transducer, acharacteristic of an aperture, and/or other relevant factors. As can beseen, the method delivers increased data granularity without the burdenof a higher sampling rate.

FIG. 20 is a flow diagram of a method 2000 of producing focused datautilizing an aperture engine 1300 according to aspects of the presentdisclosure. It is understood that additional steps can be providedbefore, during, and after the steps of method 2000, and some of thesteps described can be replaced or eliminated for other embodiments ofthe method 2000. Referring to block 2002, A-line echo data is received.In block 2004, a pre-time-of-flight resampling may be performedaccording to a first set of resampling coefficients. The resamplingcoefficients may depend in part on the range and/or flavor of focusedA-line data to be calculated, and/or may depend in part on theconfiguration of the transducer or transducers that produced the A-linedata. The resampling coefficients may designate a bump map or mayinclude configuration data from which a bump map can be determined.Accordingly, in some embodiments, pre-time-of-flight resampling includescreating and applying a bump map to produce variable-rate digitized datasubstantially as disclosed in the method 1000 of FIG. 10. Likewise, insome embodiments, pre-time-of flight resampling includes interpolationand resampling with or without a phase shift substantially as disclosedin the method 1900 of FIG. 19.

In block 2006, a time-of-flight adjustment is performed on the A-linedata according to a time-of-flight offset. The time-of-flight offset maycorrespond to a geometry of a transducer complex, a characteristic of atransducer, a characteristic of an aperture, and/or other relevantfactors. The time of flight offset may also correspond to a flavorand/or range to be calculated. In block 2008, a pre-apodizationresampling may be performed on the time-of-flight adjusted dataaccording to a second set of resampling coefficients. In variousembodiments, the second set of resampling coefficients depend on ageometry of a transducer complex, a characteristic of a transducer, acharacteristic of an aperture, a flavor and/or range to be calculated,and/or other relevant factors. In block 2010, apodization is performedon the A-line data according to a set of apodization coefficients. Invarious embodiments, the apodization coefficients depend on a geometryof a transducer complex, a characteristic of a transducer, acharacteristic of an aperture, a flavor or range to be calculated,and/or other relevant factors. In block 2012, focused A-line data isproduced in accordance with the aperture assignment.

FIG. 21 is a schematic of a focusing system 2100 according to aspects ofthe present disclosure. Portions of the focusing system 2100 may beincorporated into an IVUS processing system 106, a patient interfacemonitor (PIM) 104, and/or other components of an IVUS imaging system100. The focusing system 2100 includes a number of aperture engines1300, which perform aperture-processing tasks such as time-of-flightadjustment, amplification, apodization, and summation. Suitableexemplary aperture engines 1300 include the aperture engine 1300disclosed with reference to FIGS. 13-18. In the illustrated embodiment,the focusing system 2100 includes N aperture engines 1300, of which fiveare illustrated. In some embodiments, the number of aperture engines1300 included in the focusing system 2100 is equivalent to the number oftransducers 302 within an aperture 304.

Focusing calculations may be divided according to aperture by allocatingapertures to the focusing engines 1300. To do so, the aperture engines1300 receive an aperture assignment from the engine controller 2102. Theaperture assignment designates the aperture the engine 1300 is toprocess and accordingly designates the portion of received A-line datato be used in the focusing calculations. The received A-line data may bereceived from a transducer complex, a memory subsystem, ananalog-to-digital converter, an analog and/or digital amplifier, afilter, a signal conditioner, and/or other suitable interface systems.Once received, the A-line data is placed on an A-line data bus 2104 bywhich it is distributed to each aperture engine 1300. Only a portion ofthe received data may be relevant to each aperture and thus eachaperture engine 1300. However, in some embodiments, the aperture engines1300 receive all or substantially all of the A-line data via the databus 2104. The engines 1300 then pull data off the bus 2104 according tothe received aperture assignment. In various embodiments, A-line datathat is not part of the assigned aperture may be discarded, may beomitted, may be ignored, may have a zero value coefficient applied,and/or may undergo another culling process. One advantage to thisarchitecture is that data selection at the engines 1300 avoids the needfor complicated data steering or filtering circuitry on the bus 2104. Inaddition to potential wiring, layout, and power benefits, omittingrouting and steering circuitry allows for more flexible implementation.For example, in various embodiments, an aperture engine 1300, multipleaperture engines 1300, and/or an entire focusing system 2100 isimplemented on a single discrete computing hardware device such as ageneral purpose processor, a graphic processing unit, an ASIC, an FPGA,a DSP, a microcontroller, or other suitable computing device.

In addition to an aperture assignment, the engine controller 2102 mayalso provide the aperture engines 1300 with resample coefficients, TOFadjustments, apodization coefficients, and other parameters used toprocess the A-line data. In some embodiments, the engine controller 2102includes a set of transducer configurations used to produce bump maps.The engine controller 2102 may also include the bump maps themselves. Insome embodiments, the engine controller 2102 includes an apodizationcoefficient table containing apodization coefficients cross-referencedby emitter/transducer pair. In some embodiments, the engine controller2102 includes a time-of-flight offset table containing time-of-flightoffsets cross-referenced by emitter/transducer pair. In someembodiments, the engine controller 2102 includes a set of resamplingrates. These provided parameters including the apodization coefficientswithin the apodization coefficient table, the time-of-flight offsetswithin the table, and the resampling rates may be determined based on ageometry of the transducer complex 110, a characteristic of atransducer, a characteristic of an aperture, and/or other relevantfactors that affect time-of-flight. The resampling rates may also bedetermined based on a ratio of samples per pixel of a display unit. Oneexemplary ratio is 1:1, although other ratios are contemplated andprovided for.

As can be seen, the architecture of the focusing system 2100 enables thesystem 2100 to process multiple apertures in parallel. The apertureengines 1300 process A-line data as it arrives, and after any apertureengine 1300 receives the full A-line dataset for the assigned aperture,the engine 1300 may output the focused A-line data for that aperture.The aperture engine 1300 may then be flushed and begin collecting andprocessing A-line data for another aperture. This round-robin assignmentof apertures to engines 1300 provides high utilization (in someembodiments, full utilization of the engines) without wasted idleresources.

FIG. 22 is a flow diagram of a method 2200 for focusing multipleapertures according to aspects of the present disclosure. It isunderstood that additional steps can be provided before, during, andafter the steps of method 2200, and some of the steps described can bereplaced or eliminated for other embodiments of the method. The method2200 is suitable for implementation using systems such as the focusingsystem 2100 disclosed with respect to FIG. 21.

In block 2202, a set of apertures 304 are assigned to a set of apertureengines 1300. In some embodiments, the number of apertures within theset of apertures corresponds to the number of engines with the set ofengines, which further corresponds to the number of transducers 302 ineach of the apertures 304. For example, in an embodiment incorporatingnine-transducer apertures, nine adjacent apertures are assigned to nineaperture engines 1300. In the example, aperture 1 is assigned toaperture engine 1, aperture 2 is assigned to aperture engine 2, and soon. In block 2204, an ultrasonic dataset for a transducer 302 within oneor more of the apertures is provided to the aperture engines 1300. Thedataset may be obtained from the receiving transducer directly, or maybe obtained through an intermediary such as a memory subsystem, ananalog-to-digital converter, an analog and/or digital amplifier, afilter, a signal conditioner, and/or other suitable interface systems.The ultrasonic dataset is provided to the aperture engines 1300 eventhough it may not be relevant to the assigned aperture. Continuing theexample, a first dataset corresponding to all the receive combinationsof a first emitting transducer happens to be relevant to aperture 1only. For reference, referring back to FIG. 5, the exemplary firstemitting transducer is analogous to transducer T_(A), which is part ofaperture 502 a. In block 2206 of FIG. 22, it is determined whether anyof the aperture engines 1300 has sufficient data to produce a focusedA-line dataset. In the example, on the first pass, none of the engineshas sufficient data to produce a focused A-line dataset. Thus, themethod 2200 returns to block 2204 where another ultrasonic dataset isprovided. In the example, a second ultrasonic dataset is relevant toapertures 1 and 2. For reference, the exemplary second emittingtransducer is analogous to transducer T_(B) of FIG. 5, which is part ofapertures 502 a and 502 b. At this point, neither aperture hassufficient data to produce a focused A-line dataset.

In the example, the process repeats until the ninth iteration. On theninth iteration, exemplary aperture engine 1 has sufficient data toproduce a focused A-line dataset, exemplary aperture engine 2 has datafor eight of nine emitting transducers, aperture engine 3 has data forseven of nine transducers, and so on. In block 2208, the aperture enginehaving sufficient data produces the focused A-line dataset. In block2210, the aperture engine having produced the focused A-line dataset iscleared of stored data. In block 2212, the cleared aperture engine isassigned a next aperture. In the example, aperture engine 1 is assignedaperture 10. The method returns to block 2204 where another ultrasonicdataset is provided. Continuing the example, aperture engine 2 now hassufficient data to produce a focused A-line dataset for aperture 2.Accordingly, aperture engine 2 produces the focused A-line dataset, isflushed, and is assigned aperture 11. This round-robin assignment ofapertures allows high utilization of the available aperture engines1300.

Structural focusing as described above combines A-lines from differentspatial angles and positions. Due to these angles and spatialdifferences, time-of-flight adjustment may be performed in order toalign the samples in time. Subsequently the A-lines may be weightedaccording to their directivity angles and summed. The weighted summingcan be understood as a filter operation. In this way, weighting is doneon a per sample or per zone basis and while the weighting coefficientschange with A-line.

In addition to structural focusing, ultrasound focusing systems may havethe ability to detect motion. One method of determining motion in theimaged area is power flow. An example of a power flow algorithm isChromaFlo® (a trademark of Volcano Corporation). In contrast to focusingspatial A-line data to determine reflection strength of a scatterer, apower flow algorithm may focus temporal A-line data to determine flowrate and spectral intensity of the scatterer. In other words, instead offocusing multiple A-lines within an aperture, a single A-line is firedand captured multiple times. The change in the signal of the A-linebetween firings can be correlated to scatterer motion. It should benoted that, in many embodiments, the A-line used for power flow imagingcontains more than one emitting transducer and more than one receivingtransducer. The emitters and receivers operate concurrently, which mayimprove the signal-to-noise ratio.

To determine changes in time over the series of A-line firings, the datamay be weighted and summed. The weighting coefficients may have a rangecomponent as well as a temporal component. For example, the weightingsapplied may comprise a matched filter keyed to an expected rate ofchange, such as a typical blood velocity. This has the effect ofhighlighting motion typical of blood flow and deemphasizing other motioncommon in a biological environment. In the example, the output amplitudeof the filter correlates to the flow rate and the scatterer strength.Provided the scatterers are of similar strength, the output of thefilter is proportional to the rate change or velocity, and, for a givenvessel cross-sectional area, a flow volume may be derived. In additionto deriving flow volume, the weighted data is useful in establishingnormal flow patterns as well as vessel flows from plaque burden, stentmalapposition. These issues may prove critical to patient health.

The power flow weighted and summing process is directly analogous to theapodization and running sum performed by an aperture engine operating ina spatial mode, for example engine 1300 of focusing system 2100. As, theaperture engines are not limited to focusing spatial series, in someembodiments, the engine controller 2102 of focusing system 2100 isconfigured to operate one or more of the aperture engines 1300 in apower flow mode. In some embodiments, because the time series of A-linesdo not require a time-of-flight adjustment, the time-of-flightadjustment unit of the aperture engine or engines 1300 is bypassed inthis mode. Embodiments having a focusing system 2100 that supports bothspatial and temporal focusing may add functionality without asignificant increase in computing resources. In this way, theflexibility of the aperture engines 1300 may be leveraged to provideadded functionality without added cost.

FIG. 23 is a schematic of a focusing system 2300 according to aspects ofthe present disclosure. Portions of the focusing system 2300 may beincorporated into an IVUS processing system 106, a patient interfacemonitor (PIM) 104, and/or other components of an IVUS imaging system100. Except as noted, the focusing system 2300 is substantially similarto the focusing system 2100 disclosed with reference to FIG. 21. Whereasin some embodiments, it may prove beneficial to assign one aperture 304to each aperture engine 1300, other embodiments benefit from alternateconfigurations. For example, an aperture may be divided by focusingrange or A-line flavor across multiple aperture engines. In theillustrated embodiment, focusing system 2300 includes aperture engines1300 are grouped into pairs (e.g., aperture engine 1-A and engine 1-B),although groups of any magnitude are contemplated. The focusing system2300 may include a number of groups equivalent to the number oftransducers within an aperture. Together, the aperture engines 1300 of agroup may produce a complete focused A-line dataset for an aperture 304.Accordingly, each aperture engine 1300 produces a portion of the totaldata. The processing may be apportioned between the aperture engines1300 within the group by any suitable division. In some embodiments,each aperture engine 1300 produces data corresponding to a subset of thetotal flavors in the complete focused A-line dataset. In someembodiments, each aperture engine 1300 produces data corresponding to asubset of the total ranges 1104 in the complete focused A-line dataset.In some embodiments, each aperture engine 1300 produces datacorresponding to a subset of the total flavors and ranges in thecomplete focused A-line dataset.

Accordingly, the engine controller 2102 assigns at least portion of anaperture to each of the aperture engines 1300. The aperture engines 2102use the aperture assignment to identify and process the relevant datafrom the A-line data bus 2104. In addition to an aperture assignment,the engine controller 2102 may also provide the aperture engines 1300with resample coefficients, TOF adjustments, apodization coefficients,and other parameters used to process the A-line data.

This division of the apertures provides various benefits in variousembodiments. In some embodiments, aperture engines 1300 configured toprocess a subset of a focusing engine are physically smaller than indesigns where the aperture engines 1300 are configured to produce a fullfocused dataset. The smaller aperture engines may be implemented onsmaller, less powerful circuit devices. This may lead to cost reductionand power savings. In one such embodiment, aperture engines 1300 can beimplemented on a small, low cost, and energy efficient FPGA (fieldprogrammable gate array). In some embodiments, the smaller apertureengines 1300 can be located nearer to respective inputs and outputsthereby improving system performance. In some embodiments, the smalleraperture engines 1300 can be contained within the IVUS device 102, suchas within the transducer complex 110 or within the transmission linebundle 112. This may be referred to as processing “on the wire.”

FIG. 24 is a schematic of a hierarchically arranged focusing system 2400according to aspects of the present disclosure. Excepted as noted, thefocusing system 2400 is substantially similar to the focusing systemsdisclosed with respect to FIGS. 21 and 23. The focusing system 2400incorporates one or more hierarchical levels of aperture engines, ofwhich two hierarchical levels are illustrated (designated by first-levelengines 2402 and second-level engines 2404). Further embodiments utilizeother numbers of hierarchical aperture engines, including 3, 4, and 8,as well as other numbers of levels. A-line data is supplied to thefirst-level aperture engines 2402. The engine controller 2406, which maybe substantially similar to the engine controller 2102 of FIG. 21, mayassign sub-apertures (subsets of A-lines within an aperture) to thefirst-level aperture engines 2402. Sub-apertures may be referred to asco-arrays here and elsewhere. Various divisions of apertures intosub-apertures are contemplated. For example, an aperture may be dividedby emitting transducer, receiving transducer, and/or other suitableidentifiers. Apertures may be further divided between first-levelengines 2402 by focal range and/or A-line flavor. Furthermore, thefirst-level engines may only be assigned a subset of focusing processessuch as interpolation, decimation, resampling, time-of-flightadjustment, apodization, summation, and/or other focusing processes. Inan exemplary embodiment, a first-level aperture engine is assigned toperform time-of-flight adjustment but not apodization on a subset of thefocal ranges within a sub-aperture. Other divisions are contemplated andprovided for.

The first-level aperture engines 2402 perform the assigned focusingtasks according to the sub-aperture assignment substantially as anaperture engine 1300 performs assigned focusing tasks according to anaperture assignment. The first-level aperture engines 2402 may thenprovide the partially focused data to the second-level aperture engines2404. The second-level aperture engines 2404 may perform furtherfocusing processes including interpolation, decimation, resampling,time-of-flight adjustment, apodization, summation, and/or other focusingprocesses. In some embodiments, the second level engines receive anaperture assignment from the engine controller 2406, and thesecond-level focusing processes are performed accordingly. The partiallyfocused data propagates through the hierarchical levels of apertureengines until it reaches the final hierarchical level of the focusingsystem 2400 (in the illustrated embodiment, the second level of apertureengines 2404). The aperture engines of the final hierarchical levelgenerate the complete focused A-line dataset for an aperture.

Because, in part, of the division of processing responsibilities amongthe hierarchical levels, the aperture engines of one hierarchical level(for example, engines 2402) may be identical, similar, or different fromthe engines of another level (for example, engines 2404). In someembodiments, all the aperture engines of the focusing system 2400 areaperture engines characteristic of those described with respect to FIGS.13-18. This provides uniformity and simplicity in implementation. Infurther embodiments, particularly those where aperture engines perform asubset of focusing processes, aperture engines only include the relevantcircuitry and thus vary in structure between levels. For example,first-level aperture engines may condition data by applying a filter toenhance the signal to noise-ratio. Such filters may include bandpassfilters, matched filters keyed to the excitation pulse, and otherfilters known to those of skill in the art. If this conditioning doesnot need to be repeated in subsequent-level aperture engines, thecircuitry may be omitted, saving power and circuit area. Thisspecialization may allow engines to be implemented on smaller, moreefficient, more economical computing devices, and may allow apertureengines to be combined on a single device. The structure of the focusingsystem 2400 leverages the parallel processing advantages of the apertureengines while making accommodations for physical, algorithmic, and otherlimitations that may constrain the functionality of any one apertureengine.

For example, in some embodiments, the device selected to implement anaperture engine may not possess the computing resources to focus a fullaperture. Dividing the focusing tasks according to sub-apertures allowsdata and processing to be apportioned and distributed more effectively.In some embodiments, performance is improved by grouping circuitry nearshared resources such as a database of time-of-flight adjustments. Thus,in some embodiments, some aperture engines contain only time-of-flightcircuitry and are grouped accordingly. Other engines may have othercircuitry for performing other tasks such as apodization and may begrouped accordingly as well.

In some embodiments, levels of aperture engines, such as the first-levelaperture engines 2402, are physically remote from those of other levels,such as the second-level aperture engines 2404. These embodiments take avariety of forms. In one such embodiment, the first-level apertureengines 2402 are located within the IVUS device 102, such as within thetransducer complex 110 or within the transmission line bundle 112. Thismay be referred to as processing “on the wire.” On the wire processingmay simplify the interface between the IVUS device 102 and the rest ofthe IVUS system 100. On the wire processing may also digitize A-linedata signals closer to the transducer complex 110, thereby reducing lineloss and transmission noise. In some physically separated embodiments,the first-level aperture engines 2402 are part of a system locatedwithin a sterile field, while the second-level aperture engines 2404 arelocated outside the sterile field, such as in an adjacent observationarea. This may reduce the number of wires that cross the sterileboundary. In related embodiments where the first and second-levelaperture engines communicate over a wireless communication medium,potential avenues for contamination may be further reduced. In someembodiments, the first-level aperture engines 2402 are part of a sterilepackage. The sterile package may be designed for aseptic manufacturing,capable of undergoing chemical, radiological, thermal, and other modesof sterilization, and/or may be disposable.

FIG. 25 is a flow diagram of a method 2500 for performing hierarchicalfocusing according to aspects of the present disclosure. It isunderstood that additional steps can be provided before, during, andafter the steps of method 2500, and some of the steps described can bereplaced or eliminated for other embodiments of the method. The method2500 is suitable for implementation using systems such as thehierarchical focusing system 2400 disclosed with respect to FIG. 24.

In block 2502, a set of sub-apertures are assigned to a set offirst-level aperture engines 2402. In an embodiment, the sub-apertureassignment is performed by an engine controller 2406. Each assignmentmay further divide sub-apertures by subsets of focusing tasks, subsetsof focal ranges, subsets of A-line flavors and/or other suitabledivision criteria. In block 2504, a set of apertures may be assigned toa set of second-level aperture engines 2404. In an embodiment, theaperture assignment is performed by an engine controller 2406. Eachaperture assignment may further divide the aperture by subsets offocusing tasks, subsets of focal ranges, subsets of A-line flavors,and/or other suitable division criteria. In an exemplary embodiment,each of nine adjacent nine-transducer apertures is divided into threesub-apertures. Accordingly, three first-level aperture engines areassigned to perform various focusing tasks on one-third of the firstaperture (one whole sub-aperture each), three first-level apertureengines are assigned the three sub-apertures of the second aperture, andso on. In block 2506, an ultrasonic dataset for a transducer 302 withinone or more of the apertures is provided to the aperture engines 2402.In block 2508, it is determined whether any of the first-level apertureengines 2402 has sufficient data to produce a partially focused A-linedataset. This determination may be made by analyzing each first-levelengine 2402 individually and/or by a group analysis. Group analysis mayinclude determining whether other first-level engines assigned a relatedfocusing task have sufficient data to produce a partially focused A-linedataset. For example, the production of data may be synchronized amongthe sub-apertures within an aperture. In one such embodiment, thedetermination of block 2508 does not allow the method to proceed toblock 2510 until each of the engines assigned a sub-aperture within theaperture has sufficient data to produce a partially focused A-linedataset.

If the engines 2402 do not have sufficient data to produce a focusedA-line dataset, the method 2500 returns to block 2506 where anotherultrasonic dataset is provided. Once one or more engines 2402 havesufficient data to produce the assigned portion of a focused A-linedataset, the method proceeds to block 2510, where the first-levelaperture engine or engines 2402 having sufficient data produce therespective dataset. In block 2512, the first-level engine 2402 thatproduced the data is cleared of stored A-line data. In block 2514, thecleared first-level engine is assigned the next sub-aperture by theengine controller 2406.

In block 2516 the partially focused A-line dataset is received by asecond-level aperture engine 2404. In block 2518, it is determinedwhether any second level aperture engines 2404 have sufficient data toproduce a focused A-line dataset. If not, the method proceeds to block2506, where additional A-line data is received. On the other hand, if asecond-level aperture engine 2404 has sufficient data to produce therespective assigned dataset, in block 2520, the aforementioned focuseddata is produced. In block 2522, the second-level aperture engine 2404having produced the dataset is cleared of stored partially focused data.In block 2522, the next sub-aperture may be assigned to the clearedsecond-level aperture engine 2404 by an engine controller 2406. Themethod returns to block 2506 where another ultrasonic dataset isprovided.

Thus far, embodiments have been described in the context of RF-mode datahandling. However, the principles of the disclosure apply equally wellto baseband data handling embodiments. Put succinctly, baseband datahandling downmixes a high-frequency signal such as A-line echo data toproduce a set of complex lower-frequency signals. Because the resultingsignals have lower characteristic frequencies, digital sampling ratescan be reduced.

Transducers 302 emit an acoustic pulse with a characteristic centerfrequency f. In ultrasound applications, exemplary center frequenciestypically range from 2 MHz to 50 MHz. However, frequencies well beyondthis range are contemplated and provided for. The emitted pulse alsocontains other frequencies within a Gaussian amplitude envelope offractional bandwidth bw. The reflected pulse produced by a pointscatterer and received by a receiving transducer 302 can be approximatedby the equation:

${p\left( {r,t} \right)} = {{{Au}\left( \phi_{t} \right)}{u\left( \phi_{r} \right)}{\cos\left( {{\omega\; t} - {k\left( {{R_{t}} + {R_{r}}} \right)}} \right)}{\exp\left( \frac{- \left( {t - \tau} \right)^{2}}{\sigma^{2}} \right)}}$

-   -   where:    -   φ_(t) is the emitter directivity, the angle of incidence between        the emitting transducer and the point scatterer,    -   φ_(r) is the receiver directivity, angle of incidence between        the point scatterer and the receiving transducer,    -   A is a constant dependent on the scatter strength and the        dispersion of the acoustic wave,    -   k is the wavenumber,

τ = (R_(t) + R_(r))/V_(sound)$\sigma = {\frac{\log(0.5)}{{bw}*f}\mspace{14mu}{and}}$${{u(\phi)} = {{\cos(\phi)}{{\sin\left( \frac{\pi\; w\;\sin\;(\phi)}{\lambda} \right)}/\left( \frac{\pi\; w\;{\sin(\phi)}}{\lambda} \right)}}},$an exemplary approximation for emissions from a particular transducer.

The pulse is translated into a time varying voltage by the receivingtransducer and the resulting signal is mixed with a co-sinusoidal signal(cos(ωt)) to produce the in-phase signal:I(r,t)∝p(r,t)cos(ωt)The signal is then low-pass filtered to remove the high frequencycomponent. Similarly, by mixing with a sinusoid (sin(ωt)), thequadrature signal is generated:Q(r,t)∝p(r,t)sin(ωt)This signal is also low-pass filtered. In some embodiments, the two arecombined to form a complex amplitude, D(r,t) that includes the complexenvelope and the phase of the echo received by the transducer.D(r,t)=I(r,t)+iQ(r,t)In further embodiments, the in-phase and quadrature components are keptas separate channels during the focusing processing. After the focusingis complete, the complex envelope and phase may be derived.Env=√{square root over (I(r,y)² +Q(r,y)²)}{square root over (I(r,y)²+Q(r,y)²)}θ=tan⁻¹(Q(r,t)/I(r,t))The complex envelope is typically used in structural imaging. The phasemay be used in applications such as tissue classification, strainimaging and flow imaging.

The field being imaged can be crudely approximated as an amalgam ofpoint scatterers of varying strength and density distribution. Eachscatterer produces an echo and resulting data, which combine linearly.The focusing process measures the scatterer density/strength at aparticular point in space by separating out the contributions ofscatterers at the point of interest. In a baseband environment, this maybe achieved by rotating the phase of the signals recorded by eachtransmit-receive pairing by multiplying the signals with complexfocusing coefficients. Since the phase angle of the complex amplitudesignals is largely dependent on the geometry of the echo path (ignoringeffects due to inhomogeneous speed of sound, etc.), it is predictable.The phase of the coefficients may be chosen such that echoes fromscatterers in the region of interest are phase aligned for eachtransmit-receive combination. After phase rotation, the signals may besummed. Echoes due to scatterers at the focal point will add coherentlywhile echoes arriving from elsewhere in the medium will not. Theresulting signal is a measure of the scatterer density/strength at thefocal point.

FIGS. 26a and 26b are schematic diagrams of baseband modulatorsaccording to aspects of the present disclosure. As can be seen, thebaseband conversion can be performed using either digital or analog datasignals. Referring first to FIG. 26a , a baseband modulator 2600receives analog A-line data. The received A-line data may be receivedfrom a transducer complex 110, an analog amplifier, a filter, a signalconditioner, and/or other suitable interface systems. The in-phasemodulator 2602 mixes the incoming data with a co-sinusoidal signal(cos(ωt)) to produce the in-phase signal. The resulting signal is passedthrough a low-pass filter 2606. Similarly, the quadrature modulator 2604mixes the incoming data with a sinusoidal signal (sin(ωt)) to producethe quadrature signal. This signal is also passed through a low-passfilter 2606.

The focusing process attempts to isolate the echo signals created byindividual scatterers from the A-line data and thereby measure scatterdensity at a given location. In the baseband environment, this may beperformed by time shifting and aligning the in-phase and quadraturecomponents of the received A-line data. One skilled in the art willrecognize the similarities between baseband time shifting andtime-of-flight adjustment disclosed in the context of RF embodiments. Inbaseband embodiments, time shifting may be implemented as two distinctsteps. A phase rotator 2610 may be used to shift the analog data bydegree increments of less than one sample. For example, a phase shift of180° may shift the incoming A-line data in time by half of a samplinginterval. The phase shift values 2608 used by the phase rotator 2610 maybe based on a geometry of the transducer complex 110, a characteristicof a transducer, a characteristic of an aperture, and/or other relevantfactors that affect arrival time. Time alignment of greater than onesample may be performed using a bump map, for example, as disclosed withreference FIGS. 9a and 9b . Together, the phase rotator 2610 and thebump map converter 2620 may supplement or replace time-of-flightcorrection in the RF domain.

In the embodiment of FIG. 26a , analog in-phase and quadrature signalsare phase adjusted by the phase rotators 2610 according to the phaseshift value 2608, digitized by one or more analog-to-digital converters2612, and resampled by the bump map converter 2620 to produce digitizedbaseband A-line data. In various related embodiments, theanalog-to-digital converter and the bump map converter 2620 areintegrated into a variable-clock-rate digitizer.

In contrast to the embodiments of FIG. 26a , analog-to-digitalconversion may be performed earlier in the baseband data flow. FIG. 26billustrates embodiments where a greater portion of the baseband datahandling is performed on digitized data. The baseband modulator 2650 ofFIG. 26b is substantially similar to that of baseband modulator 2600 ofFIG. 26a , except as noted. In the illustrated embodiment, analog A-linedata is received by an analog-to-digital converter 2614 where it isdigitized. The received A-line data may be received from a transducercomplex 110, an analog amplifier, a filter, a signal conditioner, and/orother suitable interface systems. The digitized A-line data is thenprovided to digital in-phase 2602 and quadrature modulators 2604. Themodulated signals are provide to digital low-pass filters 2606. Thefiltered signals are rotated by the phase rotators 2610 according to thephase shift values 2608.

In some embodiments, the sampling frequency of the summed signals isreduced by a decimator 2616. This can be performed without significantloss of accuracy because of an advantage to baseband data handling thatmay be leveraged by embodiments of both FIGS. 26a and 26b . The processof forming the in-phase and quadrature signals downmixes the A-line datastream by the center frequency. The result is a signal with a lowereffective frequency. This lower-frequency signal can be digitized usinga sampling rate proportional to the half-bandwidth instead of the centerfrequency plus the half-bandwidth. As the Nyquist rate, the minimumsampling rate needed to avoid aliasing, is twice the highest frequencyof interest, the reduction in number of samples may be considerable. Thereduced sampling rate may accordingly reduce bus speed, data storagerequirements, clock frequency, power consumption, and/or processinghardware required for other focusing steps.

Following decimation, one or more bump map converters 2620 performfurther time shifting on the in-phase and quadrature baseband data. Itwill be recognized that decimation and bump map conversion may beperformed as part of a single process. Therefore, in some embodiments,the bump map converters 2620 receive bump maps configured to performdecimation as well as time shifting. In further embodiments, the bumpmap converters 2620 are integrated into the analog-to-digitalconverter(s) 2614 positioned earlier in the dataflow. In suchembodiments, time adjusting via the bump maps is performed prior tomodulation, filtering, and phase shifting. These and otherconfigurations are encompassed within the scope of the disclosure.

FIG. 27 is a schematic of a baseband aperture engine 2700 according toaspects of the present disclosure. Portions of the baseband apertureengine 2700 may be incorporated into an IVUS processing system 106, apatient interface monitor (PIM) 104, and/or other components of an IVUSimaging system 100. In some embodiments, the baseband aperture engine2700 provides a parallelizable focusing engine used in an IVUS system100 to leverage concurrent processing of multiple apertures in order toimprove processing throughput. In many aspects, the baseband apertureengine 2700 is substantially similar to the aperture engine 1300disclosed with respect to FIGS. 13-18.

The baseband aperture engine 2700 receives baseband A-line data, whichmay include a quadrature data component 2701 and/or an in-phase datacomponent 2702. This data may be received from a transducer complex 110,a memory subsystem, an analog-to-digital converter, an analog and/ordigital amplifier, a filter, a signal conditioner, and/or other suitableinterface systems. The received A-line data is provided to a basebandunit 2704. Suitable baseband units include those described with respectto FIGS. 23a and 23b . The baseband units 2704 may apply filtering,phase rotation according to received phase shift values 2706, complexsummation, analog-to-digital conversion, and/or resampling using a bumpmap to the received A-line data 2702 as described with respect to FIGS.23a and 23 b.

In embodiments incorporating a pre-apodization resample unit 2708, thebaseband A-line data may be supplied in analog and/or digital form, andmay be supplied as separate in-phase and quadrature components and/or asa complex sum of the two components. When analog baseband A-line data isprovided, the resample unit 2708 may digitize the analog data.Resampling of digital A-line data may also be performed by the resampleunit 2708. In this way, the resample unit 2708 of some embodiments maybe significantly similar to the pre-apodization resample unit 1404 ofFIG. 14. In various embodiments, resampling includes upsampling, such asfull upsampling and interpolated phase shifting, and/or downsampling,such as decimation. Resampling algorithms are known to those of skill inthe art. Non-limiting examples of resampling algorithms include linearinterpolation, Lagrange interpolation, cubic spline interpolation,polyphase interpolation, and/or other suitable algorithms. Thepre-apodization resample unit 2708 may resample digital A-line databased on a set of resample coefficients 2712. The resample coefficients2712 may specify a resampling rate, may specify a resampling algorithm,may supply coefficients for a resampling algorithm, and/or may supplyother resampling configuration data. In some embodiments, sampling ratesabove a certain ceiling do not improve the quality of the final focusedimage. In such embodiments, the ceiling is determined in part by aresolution or number of pixels in the final image. Accordingly, thepre-apodization unit may reduce the sample frequency of the basebandA-line data by performing a decimation process according to a ratio ofsamples per pixel. For example, the ratio of samples per pixel may be1:1.

As disclosed above, reducing the sample frequency may result in a moreefficient architecture. In some embodiments, downsampling allows forlower bus speeds, less data buffering, reduced clock frequency, lowermemory requirements for data storage, and/or a reduced power envelope.Reduced data handling requirements may also allow more flexible divisionof hardware among computing devices such as general purpose processors,a graphic processing units, ASICs, FPGAs, a DSPs, and amicrocontrollers. These advantages are not limited to improvedefficiency in the data pipeline. Reducing the dataset may also reducethe size and complexity of functional circuitry such as the complexapodization unit 2710 providing additional size, power, and costsavings.

The complex apodization unit 2710 receives baseband A-line data from thebaseband unit 2704 and/or the pre-apodization resample unit 2708 and,similar to the apodization unit 1208 disclosed with respect to FIG. 12,may perform amplitude balancing and/or apodization functions weighted toreduce effects such as sidelobe effects and grating effects. Apodizationfunctions include boxcar, Hann, Hamming, cosine, half-cosine windowfunction and/or other suitable apodization function. In someembodiments, the complex apodization unit 2710 applies a directionalamplitude adjustment, a sensitivity adjustment, and/or other amplitudemodifications. These may be specified by one or more apodizationcoefficients 2714. As the baseband A-line data may be a set of in-phaseand quadrature components or a complex sum of the components, thesupplied apodization coefficients 2714 may include sets of in-phase andquadrature values and/or may include complex values.

The resulting apodized baseband A-line data is supplied to the runningsum unit 2716 where it is added with apodized baseband A-line data forother A-lines within an aperture. When the appropriate data has beenprocessed and summed, the focused A-line data 2718 for the aperture maybe produced. The focused A-line data 2718 may be in baseband or RF form,and may be represented as separate in-phase and quadrature components oras a complex sum of the components.

FIG. 28 is a flow diagram of a method 2800 of baseband aperture focusingaccording to aspects of the present disclosure. It is understood thatadditional steps can be provided before, during, and after the steps ofmethod 2800, and some of the steps described can be replaced oreliminated for other embodiments of the method 2800. Referring to block2802, an aperture assignment and A-line data is received. The apertureassignment designates a portion of the received A-line data that isrelevant to the assigned aperture. In block 2804, baseband modulation isperformed on at least the designated A-line data. Baseband modulationproduces in-phase and quadrature components either separately or as acomplex sum. In block 2806, phase modulation is performed on themodulated A-line data according to a phase modulation value.

In block 2808, a pre-apodization resampling may be performed on thephase modulated A-line data according to a set of resamplingcoefficients. In block 2810, complex apodization is performed on thebaseband A-line data. In some embodiments that perform pre-apodizationresampling, apodization (including apodization and amplitude modulation)is performed on the resampled data produced in block 2808. In alternateembodiments, apodization is performed on the phase modulated basebanddata of block 2806. In block 2812, focused A-line data is produced inaccordance with the aperture assignment.

FIG. 29 is a schematic of a baseband focusing system 2900 according toaspects of the present disclosure. The focusing system 2900 may beincorporated into an IVUS processing system. The baseband focusingsystem 2900 is substantially similar to the focusing system 2100disclosed with reference to FIG. 21. The baseband focusing system 2900includes a number of baseband aperture engines 2700, which performaperture-processing tasks such as phase rotation, amplification,apodization, and summation. Suitable exemplary baseband aperture engines2700 include the engine disclosed with reference to FIG. 27. In theillustrated embodiment, the focusing system 2900 includes N basebandaperture engines 2700, of which five are illustrated. In someembodiments, the number of baseband aperture engines 2700 included inthe baseband focusing system 2900 is equivalent to the number oftransducers 2700 within an aperture 304. This structure enables thebaseband focusing system 2900 to process multiple apertures in parallel.

Focusing calculations may be divided according to aperture by allocatingapertures to the focusing engines 2700. To do so, the aperture engines2700 receive an aperture assignment from the engine controller 2902,which may be substantially similar to engine controller 2102 of FIG. 21.The aperture assignment designates the aperture that the engine 2700 isto process and accordingly designates the portion of received A-linedata to be used in the focusing calculations. Received A-line data isplaced on an A-line data bus 2104 and distributed to each apertureengine 2700. The received A-line data may be received from a transducercomplex 110, a memory subsystem, an analog-to-digital converter, ananalog and/or digital amplifier, a filter, a signal conditioner, and/orother suitable interface systems. Only a portion of the received datamay be relevant to each aperture and thus each aperture engine 2700.Accordingly, the aperture engines 2700 use the aperture assignment toidentify and process the relevant data from the A-line data bus 2104. Invarious embodiments, A-line data that is not part of the assignedaperture may be discarded, may be omitted, may be ignored, may have azero value coefficient applied, and/or may undergo another cullingprocess. One advantage to this architecture is that data selection atthe engines 2700 avoids the need for complicated data steering orfiltering circuitry on the bus 2104. In addition to potential wiring,layout, and power benefits, omitting routing and steering circuitryallows for more flexible implementation. For example, in variousembodiments, an aperture engine 2700, multiple aperture engines 2700,and/or an entire focusing system 2900 is implemented on a singlediscrete computing hardware device such as a general purpose processor,a graphic processing unit, an ASIC, an FPGA, a DSP, a microcontroller,or other suitable computing device.

In addition to an aperture assignment, the engine controller 2902 mayalso provide the aperture engines 2700 with resample coefficients, phaseshift values, apodization coefficients, and other parameters used toprocess the A-line data. Once any aperture engine 2700 receives theA-line dataset for the assigned aperture, the engine 2700 produces thefocused A-line data for that aperture. The aperture engine 2700 may thenbe flushed and begin collecting and processing A-line data for anotheraperture. This round-robin assignment of apertures to engines 2700provides high utilization without wasted idle resources.

FIG. 30 is a flow diagram of a method 3000 for focusing multipleapertures according to aspects of the present disclosure. It isunderstood that additional steps can be provided before, during, andafter the steps of method 3000, and some of the steps described can bereplaced or eliminated for other embodiments of the method. The method300 is suitable for implementation using systems such as the basebandfocusing system 2900 disclosed with respect to FIG. 29.

In block 3002, a set of apertures 304 are assigned to a set of basebandaperture engines 2700. In some embodiments, the assignment is performedby an engine controller 2902. In some embodiments, the number ofapertures within the set of apertures corresponds to the number ofengines with the set of engines, which further corresponds to the numberof transducers 302 in each of the apertures 304. In block 3004, anultrasonic dataset for a transducer 302 within one or more of theapertures is provided to the baseband aperture engines 3006. The datasetmay be obtained from the echo data directly, or may be obtained throughan intermediary such as a memory subsystem, an analog-to-digitalconverter, an analog and/or digital amplifier, a filter, a signalconditioner, and/or other suitable interface systems. The ultrasonicdataset may be provided to the baseband aperture engines 2700 eventhough it may not be relevant to the assigned aperture.

In block 3006, it is determined whether any of the aperture engines 2700has sufficient data to produce a focused A-line dataset. In block 3008,the aperture engine having sufficient data produces the focused A-linedataset. In block 3010, the aperture engine having produced the focusedA-line dataset is cleared of stored data. In block 3012, the clearedaperture engine is assigned a next aperture. The method returns to block3004 where another ultrasonic dataset is provided.

A method 3100 of utilizing an IVUS device 102 is disclosed referring toFIG. 31 and referring back to FIG. 1. FIG. 31 is a flow diagram of themethod of utilizing the IVUS device 102 according to an embodiment ofthe present disclosure. It is understood that additional steps can beprovided before, during, and after the steps of method 3100, and some ofthe steps described can be replaced or eliminated for other embodimentsof the method.

Referring to block 3102 of FIG. 31 and to FIG. 1, in an illustrativeexample of a typical environment and application of the system, asurgeon places a guide wire 118 in the vascular structure 120. The guidewire 118 is threaded through at least a portion of the distal end of theIVUS device 102 either before, during, or after placement of the guidewire 118. Referring to block 3104 of FIG. 31, once the guide wire 118 isin place, the IVUS device 102 is advanced over the guide wire. Referringto block 3106, the transducer complex 110 is activated. Signals sentfrom the PIM 104 to the transducer complex 110 via the transmission linebundle 112 cause transducers within the complex 110 to emit a specifiedultrasonic waveform. The ultrasonic waveform is reflected by thevascular structure 120. Referring to block 3108 of FIG. 31, thereflections are received by the transducers within the complex 110 andare amplified for transmission via the transmission line bundle 112. Theecho data is placed on the transmission line bundle 112 and sent to thePIM 104. The PIM 104 amplifies the echo data and/or performs preliminarypre-processing, in some instances. Referring to block 3110 of FIG. 31,the PIM 104 retransmits the echo data to the IVUS console 106. Referringto block 3112 of FIG. 31, the IVUS console 106 aggregates and assemblesthe received echo data to create an image of the vascular structure 120for display on the monitor 108. In some exemplary applications, the IVUSdevice is advanced beyond the area of the vascular structure 120 to beimaged and pulled back as the transducer complex 110 is operating,thereby exposing and imaging a longitudinal portion of the vascularstructure 120. To ensure a constant velocity, a pullback mechanism isused in some instances. A typical withdraw velocity is 0.5 mm/s,although other rates are possible based on beam geometry, sample speed,and the processing power of the system. In some embodiments, the device102 includes an inflatable balloon portion 122. As part of a treatmentprocedure, the device may be positioned adjacent to a stenosis (narrowsegment) or an obstructing plaque within the vascular structure 120 andinflated in an attempt to widen the restricted area of the vascularstructure 120.

Persons skilled in the art will recognize that the apparatus, systems,and methods described above can be modified in various ways.Accordingly, persons of ordinary skill in the art will appreciate thatthe embodiments encompassed by the present disclosure are not limited tothe particular exemplary embodiments described above. In that regard,although illustrative embodiments have been shown and described, a widerange of modification, change, and substitution is contemplated in theforegoing disclosure. It is understood that such variations may be madeto the foregoing without departing from the scope of the presentdisclosure. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the presentdisclosure.

While the present disclosure is directed primarily to ultrasonicimaging, the system disclosed herein is well suited to focusing any typeof phased array data. This includes data produced and collected byultrasound transducers, radio-frequency transducers, and x-raytransducers. Such applications include tomographic imaging (e.g., CT(computed tomography), microCT, PET (positron emission tomography), andmicroPET). Beyond medical imaging, focusing may take place in cellularcommunications, satellite communications, satellite imaging, radarLADAR, and other technologies. One skilled in the art will recognize theapplication of the principles herein across these and other disciplines.

What is claimed is:
 1. An ultrasound processing system comprising: firstand second aperture engines; an A-line data interface providing at leasta portion of A-line data to the first and second aperture engines; andan engine controller communicatively coupled to the first and secondaperture engines; wherein the engine controller provides at least firstand second aperture assignments designating portions of the A-line datato the first and second aperture engines, respectively; wherein thefirst and second aperture engines: receive the first and second apertureassignments, respectively; receive the at least a portion of the A-linedata; perform one or more focusing processes on the received A-linedata; and produce focused data in accordance with the first and secondaperture assignments, respectively.
 2. The system of claim 1, whereinthe engine controller further monitors to determine when one of thefirst and second aperture engines produces focused data, and provides athird aperture assignment to the one of the first and second apertureengines when it is determined that the one of the first and secondaperture engines has produced focused data.
 3. The system of claim 2,wherein the engine controller further clears the one of the first andsecond aperture engines of stored A-line data when it is determined thatthe one of the first and second aperture engines has produced focuseddata.
 4. The system of claim 1, further comprising a common A-line databus; wherein the A-line data interface provides the at least a portionof the A-line data to the first and second aperture engines via thecommon A-line data bus; and wherein the first and second apertureengines receive substantially all of the A-line data.
 5. The system ofclaim 1, wherein each of the first and second aperture engines includesan apodization unit; and wherein the one or more focusing processesincludes an apodization process.
 6. The system of claim 5, wherein theengine controller includes an apodization coefficient table; wherein theengine controller further provides first and second apodizationcoefficients from the apodization coefficient table to the first andsecond aperture engines, respectively; and wherein the first and secondaperture engines perform the apodization process based on the first andsecond apodization coefficients, respectively.
 7. The system of claim 1,wherein each of the first and second aperture engines includes atime-of-flight unit; and wherein the one or more focusing processesincludes a time-of-flight adjustment.
 8. The system of claim 7, whereinthe engine controller includes a time-of-flight offset table; whereinthe engine controller further provides first and second time-of-flightoffsets from the time-of-flight offset table to the first and secondaperture engines, respectively; and wherein the first and secondaperture engines perform the time-of-flight adjustment based on thefirst and second time-of-flight offsets, respectively.
 9. The system ofclaim 1, wherein each of the first and second aperture engines includesa resampling unit; and wherein the one or more focusing processesincludes a resampling process.
 10. The system of claim 9, wherein theengine controller includes a set of resampling rates; wherein the enginecontroller further provides first and second resampling rates from theset of resampling rates to the first and second aperture engines,respectively; and wherein the first and second aperture engines performthe resampling process based on the first and second resampling weights,respectively.
 11. The system of claim 10, wherein the first resamplingrate is determined based on a ratio of samples per pixel of a displayunit.
 12. The system of claim 11, wherein the ratio of samples per pixelis 1:1.
 13. The system of claim 11, wherein the display unit is ahigh-definition display unit.
 14. The system of claim 1, wherein each ofthe first and second aperture engines performs a summation of thereceived A-line data.
 15. The system of claim 1, wherein the systemincludes a total number of aperture engines; wherein the total number ofaperture engines corresponds to a total number of transducers within anaperture.
 16. The system of claim 15, wherein the total number oftransducers is at least
 128. 17. The system of claim 1, wherein thefirst aperture assignment designates a subset of focused A-lines withinan aperture identified by the first aperture assignment.
 18. The systemof claim 1, wherein the first aperture assignment designates a subset offocal ranges of focused A-lines within an aperture identified by thefirst aperture assignment.
 19. A method of focusing ultrasound echodata, the method comprising: assigning a set of apertures to a set ofaperture engines; providing an ultrasonic dataset for one or moretransducer within the set of apertures to each of the aperture engineswithin the set of aperture engines; producing a focused A-line datasetwhen it is determined that a first aperture engine of the set ofaperture engines has sufficient data to produce the focused A-linedataset; and thereafter assigning another aperture to the first apertureengine.
 20. The method of claim 19, further comprising clearing thefirst aperture engine of stored A-line data when it is determined thatthe first aperture engine has produced focused data.
 21. The method ofclaim 19, wherein the providing of the ultrasonic dataset providessubstantially all of the ultrasonic dataset to each of the apertureengines within the set of aperture engines via a common data bus. 22.The method of claim 19, wherein the producing of the focused A-linedataset includes performing an apodization process on the ultrasonicdataset according to a set of apodization coefficients.
 23. The methodof claim 19, wherein the producing of the focused A-line datasetincludes performing a time-of-flight adjustment on the ultrasonicdataset according to a time-of-flight offset.
 24. The method of claim19, wherein the producing of the focused A-lined dataset includesperforming a resampling process on the ultrasonic dataset according to aset of resampling rates.
 25. The method of claim 24, wherein the set ofresampling rates are determined based on a ratio of samples per pixel ofa display unit.
 26. The method of claim 25, wherein the ratio of samplesper pixel is 1:1.
 27. The method of claim 25, wherein the display unitis a high-definition display unit.
 28. The method of claim 19, whereinthe producing of the focused A-line dataset includes performing asummation of the ultrasonic dataset.
 29. The method of claim 19, whereinthe set of aperture engines includes a total number of aperture engines;wherein the total number of aperture engines corresponds to a totalnumber of transducers within an aperture.
 30. The method of 29, whereinthe total number of transducers is at least 128.